mystral: All extra points in most skills do is give you a 15% bonus chance to succeed on checks. A few skills like Perception and Concentration do additional stuff on top of that, but I don't think they're necessary.
I had max points on perception for most of the game, and I don't remember it outright unlocking some extra options in dialogue. Then again, my PC was a mage type who could read minds, so maybe that ability overlapped with perception.
Overall, character progression is much more open and forgiving than in PS: T.
If you pass a certain check for extra options, you will often be notified in the text but not told exactly which options it unlocks. That is, you'll see (for example) "[Perception] blah blah blah" when you look at something, and this sometimes causes a new action/conversation option to appear, but there's nothing on that option that suggests that it was unlocked by perception.
Catching out someone lying to you sometimes requires your character passing a perception check or reading their mind, but there are often other ways to catch them out (e.g. by gathering information from somewhere else and challenging them with it).
AFAIK mind reading and perception overlap often with respect to conversations, but not so for most objects (unless they have a "mind" of sorts to read).
Other checks I've noticed that cause extra text and/or options to appear include the various Lore types (mystical, mechanical, natural), concentration, and amanuensis.
Also AFAIK your character alone can unlock these options, although sometimes one of your characters can unlock extra options as well - however, other characters tend to unlock them based on who they are, rather than what skills they have.
