It's not a question of making the games look nicer, that can be done with DX9 too. What you might gain is a bit of performance increase if you code a DX10 Plugin, at least that's what they say about DX10 most of the time. I don't have a clue if that rule can be applied to emulation too but the performance is great enough already anyway...
Specs: Intel Core2Duo E8500 [E0] @ 3,8Ghz | 4GB OZC RAM | ATI Radeon HD 4850
