Well he wants to fight against what Tevinter is, so at the very least he can be used to destabilize it and against other magisters who enslave elves.
Dorian seems to be a bit of a trojan horse for the elves. Tevinter is one of the few places where you can actually have rich elves and no one really minds, it's also one of the few places where elves can become members in the ruling class, even if only in a limited fashion. I'd rather be a CE in Tevinter than an CE in any 'White Andrastian' nation.
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That aside, I'm not quite sure why everyone loves the city elves so much. Yes the CE origin was good and all, but is it purely just some underdog thing? Because the CE actually chose to be what they are now. The Dalish at least had the balls to pick the '...or pike off.' part of the Chantry's offer as opposed to the CE who went with the 'just roll over and die...' portion of it.
I think the Dalish's biggest, and by really far biggest, problem is that they have yet to master the art of being politely indifferent.
Every time you meet them in game they come off as unnecessarily rude. Sure you don't like humans and you want to be left alone, no need to be a dick about it and antigonise people more. Then again I also think the Dalish always come across as stupidly rude, precisely because Bioware wants to give players a 'good reason' to wipe out a clan each game.