Tiny mineral interest - what to do with it?

For a horizontal well, it may be worth hanging onto. Also, if the first well is successful, then there may be infill wells later. If you have already filed to get it titled properly, then you can sit back and wait to see what it makes. Do answer the pooling letter in the 20 days or you will get the lowest royalty. You could try selling on an auction site if you do not want to mess with it.