The other thing to remember is that you dont "have" to buy things from every collection...
If you wanna get 1 of everything, that your choice.
I collect new colors n stuff fom MAC all the time, but I make sure it's stuff I actually have a reason to buy, and want to use. Not just to buy it for buying sake. Especially since i know similar colors will come out again, if it end up being something that I have to have and I miss it, i can just wait for that.
I think for me, thats more of the fun in MAC than anything, knowing that I can wear and enjoy everything I own, and nothing really sits unused.