Why wouldn't it output 15kHz? It's not like SDTVs can take anything else. Or do you mean proper 256x224 resolution output?
I dunno, I can still sit and play Mario 64 and my mouth will hang at least part of the way open, especially when it's being emulated at some ungodly resolution and 60fps. And I think that, for instance, Virtua Cop 2 still looks pretty solid too. It's a different look, surely less realistic, but still very clean. I'm especially a fan of Dreamcast, I actually like the shininess.
Yeah, dreamcast looks mackaliciously flavourific even now. I love StarFox on the n64 as well, but the Dreamcast has... everything running at 60fps (most of the time) in most of its games. I mean, it's PS2 quality or more, in many cases. And it does 2D like a charm too. But you know what? PSX has many really pretty 2D games that look great even now. Man, should 2D make a comeback or what... I'd be happy as hell.