And, some of those "some people" are people who play on nightmare or harder difficulty. That's a fairly compelling case in itself, albeit subjective.
Now, it could be the case that all of us who have done this have all made poor choices in this regard, but that's very hard to ascertain, because you can't take a single character at a particular point in the game and run them from there till the end under both scenarios, one with and one without an upgraded tree and then compare the results.
So at the end of the day, as I said, the answer is Yes, but it is very hard to provide objective evidence that is the best of all possible choices.
As an analogy, take prodigies. I have won several times with prodigies that I wish I hadn't taken, and that I barely use. Partly because you only know if you try them. So even winning with a prodigy doesn't mean it is a good choice!
Anyway, I've enjoyed reading the debate in this forum thread as it has made aware of how differently people play.
I should add, I've won twice on nightmare roguelike, and didn't upgrade a tree in either case. But I seriously considered it. I've never got far on insane, I don't think I have the patience. I only play roguelike, which may also affect my perspective. I would rather die one hundred times at level 4 on roguelike than survive on adventure mode through multiple deaths, but that's just me.
and btw, my last normal roguelike winner spent a point to upgrade Solipsism tree. very worthwhile investment imo

http://te4.org/characters/2460/tome/a77 ... 1739b52271