1 is enough for most purchases. If there is a repaint I might not buy it or buy it and keep it sealed. A lot of things I just won't buy because the price isn't right or the size is off putting.
I think there is a strong line up of characters released in the Generations line and RTS, they are awesome enough to buy 2 of each but only on certain characters. If the packaging is in pristine condition and the box art is nice its good to have a small MISB collection as well as the loose toys. I buy one initially and If I'm happy I'll consider buying another to have MISB, but not straight away , I think maybe I'll wait for a sale, I can second guess and change my mind. This way I'm not loading myself up with stuff I'll need to off load later. Also others have a chance to buy.