I had to define myself some rules for figurines because I kept buying lower quality ones that ended up warping, or I ended up no longer liking the series. The rules are now:
1. Must be higher quality, non-posable, on a solid large base
2. Must be purchased in a pair, as in a matched set of two from the same series (e.g. Batman + Robin)
3. Must be characters I do not already own (no repeats.)
These rules have prevented me from letting the collection grow exponentially, and given a lot of variety to my toy display case. It's also probably saved me a lot of money in the long run, as I no longer snatch up every figurine I think is kind of neat.