Depends, I guess. When I play my doomed characters, crossing the wilderness without high stealth, survival, or intrinsic invisibility is very, very annoying (and somewhat dangerous, of course!). So if I have a PC that doesn't start with stealth, I might consider it worth the effort to finish the thief quest and get it. And if I get that, I'll probably grab Detect Traps as well, though I don't use it very much.
For a regular, non-doomed PC, I normally don't bother.
Hoping to win with every class, doomed. Archer, Barbarian, Bard, Beastfighter, Druid, Elementalist, Farmer, Fighter, Monk, and ULE Priest down.