Why don't you try to use them up. Remember, you can also mix two or three p/p colors together (take it out of the jar with a spatula) to create your own custom colors. This way, it doesn't feel like you have to use the same colors over and over and you won't get bored by them.
I posted a couple of examples of mixed up p/p on the PP thread (I believe I posted it there - it might be in another thread).
I second that it is very hard to resist not to open new p/p when you get them. I'll wrap mine up in a plastic sleeve and put them immediately in the fridge. This out-of-sight-out-of-mind principle works very well for me and as new p/p come out approximately every 6 - 8 months, I have always something to look forward.
I try to keep one or two neutrals (like Painterly or Nubile) in addition to one or two "fashion" colors. This gives me a lot of freedom and I manage to use most of them up. I also have at least one or two BU's of each color I buy, though I never open them back to back. Having said that, I only buy colors were I know that I will use them as I do not want to waste any product if I can avoid it.
Finally, you can also use certain colors as a cheek highlighter, so if you need to finish a product, think how versatile it is.