*sigh*
Not all SNES games are the same, there are three main reasons that a game wouldn't work on SNEmulDS.
1: The game used extra hardware in the cartridge, like the Super FX chip that handled 3D.
2: The romsize is larger than 4mb
3: The game itself used obscure coding or workarounds that the emulator isn't coded to do.
And NO, your DSi's extra memory/cpu speed are NOT being used in SNEmul, the DSi runs in "DS mode" when you use any flashcard.
But you'll be happy to hear that there's a compatibility list, you can see what games work, and what the better config is for them.
http://wiki.pocketheaven.com/SNEmulDS_Compatibility_List