One of the main reasons I use bounties is to increase the attention and exposure to a question I have.
The problem is, I myself rarely answer bounty questions, even if I have a good contribution to the question.
This is simply because when I'm bounty hunting I want to win the answer, rather than just contribute to the answer. (I'm speaking practically, and ignoring the idealistic behaviour.)
I think that upvoted answers on bounty questions should have a higher point value to encourage participation, even if the odds of actually winning the answer are lower.
rep-mining? the whole rep system is based on incentives. Why have reputation if you don't care about it? Human behaviour modification is predicated on the system of 'paying attention to what you measure'.
One true answer? we all know that the accepted answer is not always the right answer. Sometimes the right answer for one person is not the right answer for someone else. I'm under the impression that the purpose of SO is to create a repository of knowledge, not just a Q&A forum. If it's just Q&A, then sure, only the accepted answer counts, but if it's a knowledge base, then surely every good answer is worth being available?