While I wasn't using these spells I assume they work (or at least no one has ever reported them as broken, if I'm not mistaken) and I think they do not stack, but I can be wrong in this. When playing as a priest I raised my Perception skill to 5 and it is possible I drank a Potion of Perception when looking for a secret stash/wall/door where I knew there should be one. On the other hand, I'm not sure if Potions of Perception increase character's Perception because the description of the Potion of Perception doesn't say so in the Book of Magic. Anyway, this was all I needed to find all secret objects in the game.

Did you use a guide then, to make sure you got all treasures? If so, do you have a link?

I wasn't using a guide but I did search the whole world really thoroughly. If you don't want to spend hours checking every tree stump and boulder there is you could find helpful this complete map guide from Nilex[www.gog.com].

Wow that's great Kovi. Thanks a thousand :D

In case someone searches, they work and stack