"If you just had one incarnation of the most famous characters and only ever did them once then the rest of the line would be fillled with characters nobody except 600 or so die hard Muppet fans and figure collectors would buy"
---I would like to know what evidence this is based on. Just because they make 100 different Bart Simpson action figures, doesn't mean that customers need or want 100. Or even 2. I find it way more appealing- and enticing to purchase- to see ONE main character each, and ONE new character, rather than TWO main characters in different costumes and poses. I felt that way when I was a kid buying Teenage Mutant Ninja Turtles for fun, and I feel that way now as a collector. It actually becomes frustrating - and many people stop collecting an action figure line because they can't afford to keep up with variations; they just want a direct and clear cut assembly of characters and (sorry for sounding so severe) they lose hope. Customers let the toy companies lead them- until they feel cheated by the company. The demise of the ninja turtles did not come only from lack of interest- it came around the same time that toy stores were stocking "Space Walk Michaelangelo with Magician's Wardrobe and Cherry scented Bon Bons."
My guess is that a good figure will sell- an original character that catches the eye will sell. A Sweetums will sell. A "Perfectly Horrible Monster (name I dont know) will sell. That guy with the bubbles that come out of his head will sell. Digit from Jim Henson Hour will sell- and I'll even bet that they will sell a whole lot better than another Gonzo. If it says "Muppet Show" on the package, people know it's a Muppet character, even if they don't know which one it is. If they don't have Gonzo already, and they want to buy a Gonzo because they like that character, the 1st version will be just as appealing to them as a 2nd version that never existed. If the main characters are selling, then keep Series 1 nearby. Show the rest of the series' figures on the back of the packages. You aren't giving average customers much credit.
It seems ironic to me that the characters you say ordinary people don't know and won't buy are the ones that aren't on the shelves at the stores I go to. I can find Kermit and Piggy everywhere. I even have a better chance at finding Gonzo and Fozzie. But Dr. Teeth, Honeydew, and Floyd... I had to drive many miles and to many stores to find one of them. Once people buy one of these characters (Kermit), they will buy 2... then 3... even without different variations of Miss Piggy (who they aren't buying anyway.)
Good figures sell- creativity sells. Same figures, different looks, can screw up a figure line.