I couldn't live without it now, having had it for 4 years now, and I've only been driving 4 and a half! If you have it on the car you can choose not to use it. If you don't have it on the car, there is no choice, you do without and suffer. End Of! Lol!
Depends how much you value performance over comfort and how many miles you do I would say. Also, a very big factor, which you yourself have pointed out, is that a/c is a popular option. So it will be again when it comes to selling time for you. And guess what. People will choose yours last out of a bunch because it has no a/c. So although the a/c may have only been a £300 option (just for arguments sake) without it you can only sell the car for £1k less than the equivelant car with a/c.