I'm playing a very high-perception character, and found all secrets in my game so far.
I don't think I would have missed any secrets. There are so few of them, and they seem to fall under one of the following categories:
a) Random loot. But by the mid-game I was already loaded to the point where I wasn't bothering to pick up expensive loot from enemy corpses.
b) Fixed loot. But nothing unique, except for the Black Arrow sniper rifle.
c) Unlock some shortcuts. But I never want to miss a fight, I want to murder everything in my way.
d) Deacon's shop in RC. But his quality is way worse than anything you find in Core City, so what's the point.
I'll be playing with 3 PER on my next char, I don't think I'll even bother with switching to PER gear/food for secrets. Just for the ratking's trap maze.
This makes the Snooping feat (+3 PER for secrets only) the most worthless feat in the game.