Premium characters fall into 3 categories for me.
1) Characters you like. There are some characters you're just fond of regardless of cost or utility. They differ from player to player but there are certain characters people have to have in their Springfield. The value of the premium character in this instance is completely personal.
2) Useful characters. Some premium characters earn extra $ and XP on top of their premium status (like Sherri & Terri or The Wiccans), help with Springfield Heights (like Sideshow Mel & Moleman), or help with the rail yard for track pieces and donuts (like Jesse Grass, the Hippie, Dewey Largo, Uter, etc.).
3) Characters with multiplier items. Some characters come with decorations (and more recently buildings as well) that include a bonus percentage for your multiplier. Permanent premium characters like Chester Lampwick, Chester Dupree, & Frank Grimes all come with such decorations. Limited time characters like George Washington and Dwight D. Eisenhower also come with such decorations. More recently, Tapped Out has been releasing limited time characters with buildings that earn money & XP and also have a bonus percentage for your multiplier like Jaques and Senor DingDong.
I personally gravitate toward category 2 & 3 and only splurge on category 1 if there's a rebate.
