There are some games on MARP which don't have that many replays at all, in some cases they're not the most interesting of games, but It'd be nice to see more replays, how about doing some tournament which consists mainly of these less popular games, it would test players abilities to learn new games for example, as well as providing quality replays on MARP for such games.
A couple of titles I've emulated spring to mind
dommy - only has 4 replays atm
mugsmash - only 4 replays
shadfrce - only 3 (although 2 do basically say the game is retarded :-p)
welltris - 3 replays
ninjakun - 3 replays
not sure, maybe they could be mixed in with more popular games, but it'd certainly be 'cool' to see more replays for them, and in a competition environment people have more to play for. None of the mentioned games are especially demanding, so shouldn't rule too many people out of competition and I'm sure there must be other games in Mame which aren't that well covered here yet ... (unless the games I emulate really do suck that much

http://haze.mame.net