For the N64 stages it's very exciting to remake them. You get to take something and rebuild it into your own imagination of what the stage should be. The artists back then had to imply what they wanted the stage to be, we have the power now to take that idea of a stage and bring it out into almost full detail. Metal Cavern and Peach's Castle were my contributions here, and I think it's pretty obvious that I took some creative liberties with the stages... but that's because I really had to. On the Brawl stages, I don't think it'd be worth the time to really redo them and make it look slightly better than what Nintendo did. I could see other plans happening though.
Melee stages... I could see some upgrades here and there, but again... the time and effort that goes into making a stage could be spent making some new art that's unique to Project M. Personally I'm way more hyped over Bowser's Castle than my HD remakes combined. In the end this is Project M, not Smash Melee/64 "HD". We deserve our own identity when it comes to the stages and alternate skins, and I think as a fan that's what I'd want more of as well.