Erm... I probably shouldn't have much say in this as I haven't finished Point Lookout yet (there was an issue with WindowsLIVE) but I can tell you that as a stealth player, the Infiltrator is pretty average. Of course you might find it's to your liking, but I haven't used it since I left the Pitt - and I think I only tried it once there. There are other cool things to gain from the Pitt - when I was there I f*cking loved using the Man-Opener (though I don't use it so much now, me being a stealth-based character, not unless I'm just mucking about). I must agree with what you've said though - Point Lookout does seem to play better, honestly, I wasn't that fond of the Pitt, it was a nice change, but I haven't returned since. And the Pitt does give you a shed load of (I think) fairly useful perks.(Though it's yet to be decided if I'll return to Point Lookout after I've done the quests.)
My recomendation would be to get both - their both fun (from what I've played) and definitely worth the 800 points each (?) - if only for a change from the Wasteland, few added bonuses and added gameplay time.