This may be super dorky, and I don't know if it helps anyone, but I thought I'd share anyway:
This is especially for collections where Face Charts are also released, mainly because I LOVE Face Charts and like to try them out...
I never buy from collections right when they're released, because I know if I did I'd over-buy.
Instead, what I do is, I make a list of the products in the collection, then I go through them and write down "dupes" that I could use in their place from my own current collection. Then I re-create the Face Charts or looks that I see from people here, etc., using my "dupes" and I see which of the products I already have will work for me in place of the LE items, and which things I still really 'need'.
Then of course I read Specktra religiously which also points out which products aren't so hot vs. are amazing!
Here's an example: I really wanted Solar White from Cool Heat. So, I used White Gold p/g in place of it for about a week and decided that those two were not the same after all and that Solar White was something I really could use-now I have SW and I LOVE it, AND that was the only thing I bought from Cool Heat!
I really hope that helps someone!