Sorry to bring this up again since it seems the discussion has moved on but, one important fact missing from the 'transwarp didn't work' argument is that it did work.
Captain Stile's said, paraphrased, If they try to get away with warp drive they're really in for a shock. We see the transwarp systems come online and the computer even audible confirms it is ready to go.*
The only reason it didn't work in ST3 is because Scotty sabotaged that circuit by simply removing some chips. (*which if we really want to pick at something - what about the Excelsior computer not discovering the missing chips during start up???)
So what about after that, was TWD completely scrapped simply because someone removing some chips renders it useless? I doubt it. Future ships clearly somehow managed to achieve greater warp factors and TWD is probably the reason why.
Oh, and what about the Vengeance... in my head canon Khan gave that ship TWD.
Agreed about the Vengeance. That sure sounds like some sort of Transwarp tech. But I have no idea why that technology wouldn't have been used later after III. I'm just going with A) the lack of canon evidence that it was B) the fact that VOY brought the tech back and C) the fact that supplementary (non-canon) materials by people involved with the show confirms this.