I don't know about you guys - but I try and find all the little secrets in the game. I've been trying to find all the little purple hidden stashes that I can.

 

In my first playthrough, testing everything out in Easy mode, I went with a rogue with fairly high sneak, might and dex primary, with perception secondary. I found quite a lot of the stashes - some of which were quite helpful with unique weapons and such. Second playthrough (normal mode), I built a custom adventurer at an inn that fulfilled this role. He didn't have as much perception, and was not picking up on most of the stashes I had found earlier - though picked up some others I had not found. In another start, I maxed sneak and perception, and found some new stashes I had not uncovered before, but couldn't find some stashes or switches I had done previously.

 

So, the question is - what goes into making a successful scout mode check on finding these stashes?

It's mechanics skill as far as i know.

Yup... it's a bit counter-intuitive, but mechanics is required for finding hidden "purple" stashes, but this will only be activated while in stealth mode... you could even have 0 in stealth and still find hidden stashes, just hit the stealth mode with a high mechanics and you'll find everything. Bit silly imo but whatevs.

I think they merged sneaking and searching to the same animation due to the similarities in action. Either way you have to be slower and more careful. 

From a D&D 3.5 perspective:

 

Perception is Spot, Listen, Sense Motive, and Wisdom.

 

Mechanics covers Search, Disable Device, and Open Locks.