I think it would be fun and interesting if bounty values could be set to any integer value and everyone had to strategize about setting theirs. If I could right now set a bounty of 251, that would be a big advantage because my Question would be above all the 250's... until everyone else thought of that, of course.
On most SE topic sites, this feature would just be a needless complication, but this is the MATH site! Imagine how OCD some users would get analyzing the resulting distribution of bounties and deriving concordant optimization strategies. And imagine the fun the rest of us would have watching them! :-)
I'll also take this opportunity to repeat a popular suggestion that hard Questions that carry big bounties and will require thoughtful detailed Answers be allowed longer bounty periods. Many users want this, and I've never encountered any counter-argument that didn't amount to "but that's not how we've always done it!" This improvement is long overdue.