New Adventures under the budget of the original series

Gosh... There are a lot of stories that would have been very difficult, if not outright impossible to do on screen because of the visuals alone, Parasite is one that leaps to mind almost immediately with Sky Pirates, Blood Heat, Time's Crucible, Transit, Set Piece, Lucifer Rising, The Left-Handed Hummingbird, Lungbarrow, Eternity Weeps and Revelation following quickly afterwards.

Still, there are more than a few stories here or there that could've made the transition across:

• Exodus strikes me as something that could've been told in 1990 with little issue.
• Sanctuary could have been easily accomplished to a tee. The Doctor and Benny note how where they've arrived looks like Necros, they could have reused Bolinge Hill Farm in Hampshire as a filming location.
• Nightshade's main hurdle would have been the tertiary console room and maybe the Sentience at a stretch, the rest was conscientiously written with the televised Quatermass in mind.
• Parts Three and Four of Shakedown have already been put to video and the wonderful bookends with the Doctor, Benny, Roz and Chris wouldn't have been too difficult.
• Falls the Shadow would have been very heavy for the visual effects department's depiction of interstitial space, but it's no harder to film than Sapphire and Steel or Ghost-Light. The gore would have to be toned down significantly though with particular loss of emphasis on Paige being tortured and the Doctor and Winterdawn being ripped apart by a storm of glass.
  
• Human Nature, I think... The novel's quite a bit different from its televised counterpart, but I think it could have been done as it was.
• Legacy would've been very simple to do too, Peladon lends itself rather well to television and it would've been nice to see a nineties update of it.