My feeling is that they're more likely to keep the classic look and feel rather than tart it up, but that's just a guess.
I second that, id has never cared about touching up their old games, they just make make improvements to the new ones.
Every time they re-release the classics for some new system, it's the exact same graphics and gameplay from the 1990's. It's like overdone nostalgia, but I guess some people like that, if not most people.