Well, in fairness, if you have a "pure" rogue, then it's mostly going to be a support character anyway. But that Perception gives you increased sense range, so your party is surprised less often and can better prepare for fights; it gives you more starting AP in a fight, so that if you've stealthed up near the enemy you can incapacitate or cripple at least one or maybe even two enemies in the first round; and it gives you better trap detection, like you said.
The value of having one (or more) enemies too busy drooling on their own feet to hit you with the pointy sticks can't really be overstated in most (non-gimmick) fights. That one spot with the sleeping goblins? Very tough fight for a party to take face-on. Very easy with half the goblins stunned, blinded, and knocked over.
