To say "Arcade games are just too powerful" makes no sense. It's like saying "Console games are just too powerful." For one, the games don't really have power in any sense of the word, but more importantly, arcade machines, like consoles, vary in their specifications. Some arcade machines, like the Neo Geo, can be emulated on the DS, and some, like say the CPS-3, or let's go nuts, the Triforce, can't. Plenty of machines probably could be emulated on the DS, as shown by
MarcaDS, which supports quite a few different machines.
X-Men might be possible to emulate on the DS, but it's a stretch. It ran on a 68000 at 16MHz (the Neo Geo ran at 12MHz on the same processor). Maybe with no sound and still (much) below full speed, probably not worth it. Same goes for AVP and Marvel vs. Capcom, those were both on the CPS-2; possible, but not practical or enjoyable.
Are you aware that Knights of the Round and Captain Commando had SNES versions? You might want to try them out in SNEmulDS, I can't vouch for how well they'll work, but give it a shot. That said, a CPS-1 emulator (which is what KotR and CC ran on) would probably be pretty workable on the DS; it had a 68000 ranging from 8MHz up to 11 (not sure what they were clocked at for these particular games), which even leaves room for sound; a 3.6MHz Z80 should be pretty manageable, games which used just the YM2151 might work out OK.
Just looking at the Wikipedia article on The Simpsons, it looks like it would be extremely workable on the DS, except for using Konami's own custom processor, which nobody (especially DS developers) really has that much experience with. If someone worked up a core for that, which only runs at 3MHz, there'd probably be plenty of room for at least one (the YM2151 again), probably both sound chips.
After all this though, there's still the resolution to worry about. Quick glance, the CPS-1 outputs at 384*224; that is, it's as wide as both DS screens put together when you turn it sideways. The height you can probably fudge, but losing 128 pixels of horizontal action is going to hurt.