I did a UOA on a new engine because I was curious about what was in there, and I felt it would set a "worst case" baseline on my vehicle. I figure that the numbers would go down from there, but if they went up on the next UOA it would make me pay a little more attention.
In my case, it actually drove me to have Terry Dyson look at it and I ended up dumping the oil early. So for me it helped me make a decision that I was on the fence with. In the grand scheme of things, I learned a bunch of stuff that I would not have if I went "sans UOA". So that was worth my $$. I also thought I would have regretted not doing it, so the $20 was worth it to me.