Wishing wells...

[Renevent]

I noticed there are quite a few wishing wells scattered about the world that ask you if you want to throw all your crystals in for a reward. I have about 32 crystal at the moment, but being a mage crystals are VERY valuable to me. Also, the reward from the wells seem to be either set in stone (not random) or based on how many crystals you throw in. Is this true? Or do certain wells produce different grades of items with an increase of crystal "donations"?

What is everyone's tactic for these? Do you wait until end game when you have upgraded all your spells and don't need crystals? Is there another way of getting good supply of them that I don't know about?

Also, does anybody have a list of wishing wells and which give what items?