This would change my work from a hobby to being a business. If someone pays for a ticket, the roles change a bit. The person who pays will expect something from you. I personally would not do that. If you like what I do, send me a beer afterwards. Or a gittip or a flattr. But don't pay me money.
> I think maybe each bug could have a pot where people could to put an amount, and if a developer fixed that bug and enough people agreed he would get that pot.
Except leave out this part:
> That way developers could pick the bugs where people are willing to put their money where their mouth is.
Instead, completely hide showing how much money was donated to a bug. From everyone. When a developer fixes a bug, they may get a nice surprise for their contributions, that may further encourage them to work on issues.
A little like GitTip, but you're tipping whoever solves an issue, ahead of time. And because it's invisible, it doesn't make your hobby feel like a job because you don't know which issues are worth the most. (although it may be possible to guess by issue popularity)
Or how about this... There's a hidden pot and every user can only contribute the same amount of money (say $1) to the pot. This way, the value of the pot would more likely reflect the community consenus of issue value to the project.