Okay, clearly you are the opposite from me on everything (and are too busy having a vendetta against girl wonder (which is full of very nice people, thanks) to argue the points I've made. So fine, decide supporting cast and Kara actually having villains and doing something OTHER than being Supergirl 24/7 while whining about how she hates being Supergirl= no independence. (and Lois Lane's appeared, what, once? twice?) After this I'm done.
BUT, on sales. Kelly's sales may have been higher initially, because Kara was still shiny and new, but they were plummeting faster than Bush's approval ratings. There's a REASON Berganza did his pathetic "Oh girls, please read my comic" thing. And Puckett made them plummet even more.
Now that Gates is on, sales are actually not only stable for the first time, but increasing. Yes, they're lower, but ALL comic sales are lower. We happen to be in an economic crisis, and that's affecting comic sales.
Here's a pretty good history of Supergirl's sales and the current good sales of the Gates run:
Also, Boomer and Wonder Girl are not a supporting cast. At all. They are two people who occasionally showed up in the title. Wonder Girl was a character who showed up far more in other books. The Supergirl title had no characters that were primarily theirs. And it was ONLY TWO PEOPLE. Who were BORING.