According to "developers working on the system", games running on the Nintendo 3DS can look (and perform) even better than those we've seen on one condition: they lose the 3D.
That's what a report on IGN says, as developers "could theoretically use the extra processing power for additional texture passes and more complex object and environment geometry, or even up a framerate from 30 frames per second to 60".
To be honest, I hadn't even considered that. But they're right: it takes processing power to render the images in 3D, since they're essentially creating the same image twice (one for each eye), so freeing that up should indeed result in better-looking games with more stuff on-screen.
Whether a developer or publisher would risk bypassing the system's main selling point is up for debate, but surely somebody is willing to take a chance considering the potential benefits. I know I'd trade 3D in a lot of games for smoother performance and better graphics.
Nintendo 3DS: Your Questions Answered [IGN, via Go Nintendo]