Another Planescape: Torment game is at the top of my wish list, though a realistic budget for such a project would be far beyond the $1.5 million that Double Fine has drummed up so far.
I think a small games project would be a good idea. For Obsidian to grow beyond where it is now, you guys really need your own IP, and a smaller project would allow you to experiment with original IPs without the enormous risk of a Triple-A endeavor.
When I was at Obsidian, there were quite a few good small game ideas generated by myself and others. I recommend picking the best of those, filming a pitch video to post on Kickstarter, and then see how the public reacts. A small team composed of a programmer, designer, 2 artists, part-time sound designers and QA, could complete a pretty decent small games project in less than 6 months for under $250,000. If you get extra money, resist the temptation to pour it into the one project (scope control), and instead start up a second team working on another project.