To me Outrun is kind of done, in that Outrun 2 is a perfect game.
In my opinion there is nothing that could be done to improve Outrun 2, or Outrun Coast to Coast (my most-played PSP game). Graphics would obviously improve, but honestly to me the graphics of Outrun are not super important. Maybe I'm wrong?
Hang on.... now that's my all-time favorite Genesis game, and I'd kill everyone I've ever loved to play a new one on Vita.