Cowher would be a definite upgrade over Wanny. But he's still overrated as a coach. He's been badly outcoached in each of those AFC Championships he's lost. The one they lost to New England was inexcusable: underuse of Amos Zereoue, horrific special teams play, etc. In fact, unless I'm mistaken, he's lost them all at home. (a quick look at nyjunc's post verifies that at least someone is with me on that stat)
It's irrelevant, though: Cowher signed a long-term extension before this year, and unlike Wayne Huizenga, the Rooney family is totally unwilling to eat that money.