The best well is the Wishing Well in the Land of the Giants (Eeofol), but I would strongly advise you to put up GM Protection from Magic before you use it. I'll leave you to find out why.

There is an NWC dungeon in the game, but you can't get to it until almost at the end of the game, and you'll find it's virtually useless when you get there - certainly useless for your purposes. There's no equivalent of the +30 levels well, and there's no Fountain of Youth. There are the usual stats-boosting wells, altars, etc., but there is nothing exceptional in them. Among the most useful items in the land are the Challenges. These give you skill points bonuses, but I'll leave it to you to find out how they work.