No I wouldn't have liked a boyfriend for Dawn, for starters I like the point Vamp Jenny made about not everyone having a romantic life at that point in their life, and secondly I kind of feel that with everything going on in Dawn's life (knowing that she was some created mystical property only apart of reality because her 'sister' is a superhero with a super-secret identity and in constant mortal peril, not to mention Buffy dying, Buffy-bot, Buffy returning...) It just seems like piling all of this on top of normal teen angst romance would have been the furthest thing from Dawn's mind (and even if it wasn't, she was a teen girl after all, it seems like it would just have been too much of a mess to have her in a relationship... because of her personal stuff and because of Slayer stuff... unless she could have dated some kind of supernatural dude who knew about all that, but at that point in the series that had just been done to death, hadn't it?)
So in short, I prefer Dawn single and struggling to find her place in a world to which she actually knew that, regardless of memories, she was actually quite new to.
🙂