Campaign rates go down quickly and up slowly. Participants have to accept that. I do not like the idea of pegging rates to usd because this undermines bitcoin as a separate "currency".
It does undermine like you have said but this is the only long-term and viable solution. Yes it's the pain in the ass to switch all the time when Bitcoin drops or rises $50. Campaign managers don't have this much time and we need to understand this.
I don't see anything of a big deal to peg it to the usd and just pay out the BTCs. It saves managers a lot of trouble and it also makes participants pockets a bit fuller.