I know another game and having a forum with quest guides and other guides didn't affect the gameplay AT ALL.
people stop interacting in-game as much and miss out on the multiplayer part of PlaneShift
No they don't a friendship isn't only on giving information to the other (that's called teaching). And sometimes, people become "stalkers" which isn't very good.
focusing instead of PPs, trainers, quick quests answers to get the rewards, etc.
Do you know what a real MMO is ? Well it isn't just chatting between people and seeing characters move on the screen which are animated by people. It is to do things together, interacting (not just in the way of chatting). One thing you could do is make much more difficult places to get there and you would only be able to go there if you are with friends. And not difficult in a way that it is hard to find your way, in the way that there are many powerfull creatures attacking you on the way.
How to make money? How to roleplay? How to create guilds? Things that won't spoil the game
I could do that, but it would all fit on an A4 page:
How to make money? Mine platinum or gold
How to create guilds? Read the manual
How to roleplay? Simple, act as if you were IN the game, not playing the game.
[EDIT] I re-openned my website so that people can look at it. I removed the section "Quest" (like you said earlier in this post)