I can't explain why, but I really love when I have a favorite figure and can find a mini or micro version of the same toy or character. It's kind of like the character having a figure of himself. My most recent addittion to this part of my collection was the Action Fleet version of Boba Fett that came in a big auction lot I won:
I also have Thor, Captain America, GI Joe Green Beret, Great Mazinger, Mazinger Z, Grandizer, Green Lantern, and maybe a couple more characters with 'mini-me' versions.