I have about 6000 rep right now, but I have kind of lost my will to participate in this site. After thinking about it a bit I realized that one easy way to use my current rep is to do the following. First, keep my rep above 200, the minimum needed to get a free 100 rep in any new stack exchange I join. Second spend the rest on bounties here. I obviously already posted three bounties in the last week.
However, there are many ways to do that.
I could spend 50 per bounty, leading to most people not looking at the bounty. This is made worse by the fact that many of the upvoted unanswered questions are upvoted but not answered since they are hard to answer.
I could instead do 500 per bounty, but even if I drain my account that is only 12 or 13 questions.
Therefore I need an answer that is somewhere in the middle. What is a heuristic I can use to assign bounties to questions to maximize the total number of questions answered on this site that would not be answered without the bounty?
Edit: I am targeting questions that are unanswered, has a positive score, whose askers have visited the site in the last 30 days. My estimate of the difficult of the question is a function of the number of days the question has been unanswered times the score. My rationale is two fold. First higher score questions imply many people looked at the question, liked it, id a little research, and probably gave up. This means higher score questions are harder and need a higher bounty. Second, the older a question is, the harder it is to answer, therefore the higher it's bounty.
Using this system I have guessed the appropriate bounty for each of the following questions:
Does twice the planet radius mean two bands of desert per hemisphere?: 500
Plausible altitude for my planet's ring?:500
How different, geographically, would Western North America look if the ice ages lasted 14 million years:500
What would the climate of a Pangaea-Ultima-inspired world be like?:300
Could these Humanoid/Reptilian shoulders support legs?:300
How to Create Tidal Tsunamis:300
Could a bird respiratory system still work without the same bone structure as a bird?:50
Could a bird respiratory system fit in this humanoidish body?:50