I'm only a completist in two lines: Star Wars and Muppets (although I could really care less about the ridiculously rare items -- I can't justify spending that much money on little bits of plastic). I also collect the LOTR and Marvel Legends figures but only pick up the ones I really like from those. As for the Muppet exclusives, I'm only picking up the NEW figures, such as Super Scooter (which I'll be getting sometime soon) and Chef w/ Lobsters (which I already have).
Anyway, how I collect (as in the physical act of 'collecting') Muppets is just find out the 'release' date, show up at Media Play or Suncoast sometime in that day's afternoon, and just look. Of couse, it's usually by luck since it took me several weeks to locate series 6. But, you know, if you look hard enough you don't have to do that. I've seen repaint Janice & Clifford in the past month on the shelves, so they aren't as rare as they can seem to be -- you just have to find the stores that don't sell out quickly (such as a Sam Goody in this major mall here).
I'll buy every figure they release normally, as I (and I'm sure the vast majority of you guys) have been waiting for these figures for my entire life.