To get back to the heart of this thread: What games are the candidates most in need of "tweaking"?
I wouldn't consider Space Harrier as strong a candidate as something like Impossamole, where the (coldet) collision detection needs some finessing. Or Order of the Griffon, where the music cuts out prematurely at the onset of each melee (battle).
Sadly, Ballistix can never be "fixed" because it is fundamentally a lame game.
No, I'm lying. I would love Space Harrier to be tweaked (if only to include OUI OUI JUMBO as a playable character).
Altered Beast had its controls tweaked by Tom.
Strider and Golden Axe would benefit most from 60fps scrolling.
Backup saving being implemented for games that only support passwords.
Shapeshifter would be easier for some people to get into if the controls were tweaked.
Bonk's spin in Revenge and Big Adventure could be tweaked back to Adventure-style.
Regional differences could be merged, so that the titles such as the Bonk games use the original graphics.
Tom proved how well the PCE handles extreme speed boosts in SFII'. A balanced boost to the factors that would result in the equivalent of Turbo speeds for the game would be cool. Even if you have to load a different rom for a different speed.
Infinite or increased credits for arcade ports would broaden the appeal of many games.