CGI: Gallifrey

Reading between the lines of the article in the most recent issue of Doctor Who Magazine, about the new effects and location scenes for Logopolis' Blu-ray debut, there is a suggestion that it is intended that each box set might have at least one story with new visual effects. Both of the sets already released have had one story with new effects - Revenge of the Cybermen in the Season 12 set, and Castrovalva in the Season 19 one. New VFX would obviously be a good marketing ploy for those who don't see the need to replace their DVD collection with costly box sets just for some new documentaries which might turn up on You Tube one day anyway.
For Logopolis, they have not only added new CGI material, but they have also shot alternative scenes at the location where the story was originally to have been filmed - Jodrell Bank in Cheshire.
Optional new CGI effects have been on offer since the earliest days of the DVD releases. The first release to have them, back in 2002, was The Ark in Space, where viewers could have the model shots of the space station and the rocket ship replaced.

Doctor Who fans idolise the VFX people and have always forgiven them for the odd dud effects shots, and some people thought that replacing model shots with new CGI effects was tantamount to blasphemy. However, no-one really complained as the new effects were entirely optional, and had to be chosen from the "Special Features" menu - so not even the default setting. Compare with the outcry when the first Star Wars trilogy was released with new effects, plus some major changes - such as replacing the actor who originally played Anakin Skywalker (Sebastian Shaw) with Hayden Christensen - and purchasers were denied the option of seeing the original versions.
Another early release to be given the CGI treatment was The Dalek Invasion of Earth, where the shot of Battersea Power station was replaced, as well as the more substantial upgrade of the Dalek spaceships - from a pastry cutter dangling on strings in front of a photo of the Houses of Parliament, to snazzy Century 21-style saucers, which went on to be used in the series itself when it returned to the screen in 2005.

Over the years a number of other DVD releases have offered these optional CGI effects - often alternatives to model shots or fancier laser beams. Some releases have included new sequences that were poorly realised in the original broadcast version - such as the destruction of Irongron's castle in The Time Warrior, or of the freighter in Earthshock.
For the most part, I have been perfectly happy with the new effects, and will generally watch the discs with these switched on. I can understand why purists might object and insist on watching the stories as they were originally shown - but unless you are watching the 1960's stories on an old 405-line TV set, that takes half an hour to warm up, then you aren't actually viewing them as broadcast anyway.
Why put up with the pastry cutter Dalek ships when you can have the lovely saucers?
One VFX which was certainly worth replacing was the giant Mara snake which features in Part Four of Kinda. For the DVD release, just this one sequence was upgraded. Instead of the patently plastic pink thing we saw back in 1982, we now have the option of seeing a much more impressive, far more realistic snake.

One story I am in two minds about, though, is The Invisible Enemy. This had some fantastic model sequences, courtesy of the great Ian Scoones. The DVD release retains some of these but replaces many others. Whilst giving Titan a murky yellow smog for an atmosphere might be more scientifically accurate, the original sequences just look much better. However, I was never happy with K9's blaster effect, and it is nice to see that they got rid of that obviously pre-cut pillar which Leela asks the mechanical mutt to knock down into a barrier. The new effects also sort out the mistake of having the Bi-Al Foundation shown already damaged before the space-shuttle crashes into it.
And whilst the exploding castle is far better than the stock footage of a quarry explosion that was originally used for The Time Warrior, the new CGI sequence looks a little cartoon-y.
I'm very glad they chose to offer new effects for Revenge of the Cybermen, as it has always jarred when you watch this after viewing The Ark in Space with its new effects turned on.
It should be noted that even having millions of dollars to spend, and companies of the standing of Industrial Light & Magic or Weta on board, does not guarantee an escape from dud VFX shots.
I read an on-line article recently titled "The 50 Worst Special Effects in Movie History" - link below - and there are some very big movies included in the list, including work from the likes of George Lucas, Steven Spielberg and Peter Jackson.
https://www.complex.com/pop-culture/2012/11/50-worst-special-effects-movie-history/
Having seen most of the films on the list, I found myself nodding along in agreement throughout, and even guessed some of the ones that would feature in advance.

So, what stories still to be released on Blu-ray might get the new CGI treatment? There's an interesting shot in the making-of documentary on the DVD release of The Web Planet, of one of the Larvae Guns firing. It appears to have added CGI, which leads me to wonder if they once considered having optional new effects for this story. Presumably the clip comes from a test sequence. Apart from the Larvae Guns, there aren't really that many FX shots in the story that need replacing, however. The Chase might benefit from some changes - such as a new version of the Mechonoid city, or an enhanced Dalek-Mechonoid battle sequence. That Mary Celeste model certainly ought to go. It wasn't until Genesis of the Daleks that we actually saw the Daleks fire their death ray, so Dalek firepower could be upgraded for any of their stories prior to this. (Day of the Daleks has a whole CGI VFX-heavy Special Edition already).
Two other B&W stories that might benefit from VFX upgrades are The Dominators, and The Seeds of Death. The former has some rather poor model work in the first and fifth episodes. The latter has a couple of lacklustre rocket base models - one for Earth and one on the Moon, which appear to be the same model with a different backdrop. The story lacks any good establishing shots of the moonbase, where more than half the story is set.
Pertwee stories might be harder to work with, as many of them have picture quality issues at the best of times. CGI sea serpents and Drashigs might be an idea for Carnival of Monsters, and I can't be the only one who'd like to see the 10,000 strong Dalek army in Planet of the Daleks not realised using a couple of dozen Louis Marx toy versions.
In the same way that Revenge jarred after watching Ark, so any K9 story looks bad after seeing the blaster effect used for The Invisible Enemy and for The Invasion of Time. I'd like to see all his stories upgraded if only for this one effect to be improved.
One other Tom Baker story I'd like them to tackle - again for just one FX sequence - is The Android Invasion. We get a very good look at Guy Crayford's spaceship, and it looks absolutely nothing like a Saturn 5 rocket - stock footage of which they use for the spaceship's lift-off.

It actually hurts to watch.
There are fewer stories which would benefit from upgrades once you get into the 1980's. A few Davison stories have already been given the new CGI option - including Earthshock, the whole of the Black Guardian trilogy and The Five Doctors. Regarding the former, there were two Fiona Cumming directed stories where she went back and re-edited them into slightly condensed movie versions, with new VFX. Enlightenment works quite well, but the same can't be said of Planet of Fire, which has too much material cut out of it, as well as being given a whole new prologue sequence that doesn't fit well at all.
No amount of fancy new CGI effects can save some stories, however. I'm looking at you, Twin Dilemma and Timelash. I'm sure Colin Baker would love to have his costume CGI'd out from every one of his episodes.

Of course, the one story we would all love to see given new VFX - one which even the purists would accept - is Invasion of the Dinosaurs. I've written about this before, but that was a while ago so I'll repeat. There aren't actually that many dinosaur scenes in the story where you also have people in shot. Scenes where you see the Doctor or the Brigadier in shot with a dinosaur are few and far between - and in some cases the actors are only seen in long shot. There is no reason why the dinosaur sequences couldn't be cut out completely and replaced, with new actors playing UNIT soldiers, such as the scene early in Episode 2 where they fire at a T-Rex, and they could employ body doubles for Pertwee and Courtney for those long shots.
I'll be sorely disappointed if, when they get round to releasing the Series 11 Blu-ray box set, we don't get some decent CGI dinosaurs.