Actually, I went through a moment maybe 5 or 6 years back where I went "WTF?" and decided to think about what I loved. Money was tight at the time, and I felt like I needed to bring more focus to my collecting. I was buying a lot of non-TF transforming toys reflexively, and not getting much joy from them. I thought about it for a while, and these are the self-imposed 'rules' that work for me:

1) No repaints. I wouldn't say that I never break this rule, but there are usually pretty compelling reasons when I do, so it is infrequent. If a toy has play value, buying the same toy in a different colour isn't going to improve the play value.

2) What lines do you love? For me, it was Transformers first, Masters of the Universe second, and M.A.S.K. third. Everything else has been dropped, and things I want from the latter 2 lines now come up so rarely that it doesn't eat into my budget in a big way.

3) Avoid toys with little or no play value. My hobby is all about the play, and if there is not something compelling about the play value of a toy, I'll avoid it. If it is ludicrously cheap I may sometimes buy one just to have an example in my collection, but will usually avoid. Things like Bumper Battlers, merchandise like costumes or toothbrushes, Armada Laserbeak, etc.

4) Where possible, wait for the sales. This one probably saves me over $500 a year.