Apparently in in the original ED you could farm respawn points for XP, but in DKS, it seems they've fixed the loophole - the respawn areas are still there, but after a certain number of respawns, you start getting 0xp for each kill.
At least that's what I found with every respawn area I discovered (and I've seen others on these forums confirm it).
As for Wisdom, I don't think it's worth it. Consider that each skill point you spend in wisdom only gives you 2% more experience. That means you'll have to advance 50 levels AFTER spending that point on wisdom to get the point back (50 levels * 2% experience = 1 full level due to the wisdom bonus). Given you're not going to get much higher than level 45, you'll be losing heavily on skill points, especially since you need to already be pretty high level in order to max out wisdom in the first place.
OK, so levelling does give other advantages beyond skill points (such as ability points) but it's the skill points that are the most useful. And to get maximum advantage out of widsom, you need to spend the points on it as soon as possible, so you get the most XP advantage through the rest of the game - and skill points are in very short supply in the early parts of the game.
But mindreading - definitely useful. You'll get far more skill points back than you spend, especially in the later parts of the game. For example, almost every opponent in the Hall of Echoes gives you a skill point if you mindread them.
Skill books are also plentiful in FoV (often as quest rewards) but there's as many skill points to be gained from mindreading in FoV as from the books.
Finally the mindread cost varies with different people - basically if mindread is going to cost a lot of XP, then you'll get something good (skill point, item etc). If it costs little XP it's not worth it (you'll get some useless personal thought).
