Let me get this out of the way first: I think that Seattle is a better place for an NBA team than Sacramento. Seattle is bigger (a million more people in the metropolitan area, 15th-largest in the nation to 22nd, plus within TV-package and driving distance for residual Vancouver basketball fans) and has a richer basketball history (the Sonics were ingrained in Seattle's DNA in a way that the Kings have not been since moving to Sacramento in 1985; plus, Seattle grows NBA talent out of proportion to its population). The Kings in Sacramento are more like, say, the NHL Kings in LA -- present but not beloved. But I recognize that that may just be my bias talking; discount at will.
What I really want to say is that even if Seattle gets another team, a resurrected Sonics, it will just be a cherry atop a giant bowl of shit. Part of me thinks that this is all just a ruse by David Stern to extort a bit more money from Sacramento for the Kings (and all the better that his dupe is Seattle, the city that had the temerity to refuse him the last time he came demanding money). Even if it works, though, it serves the NBA's nefarious interest. A large part of the NBA's business model today is to increase the value of its franchises by demanding nine-figure stadium subsidies from local governments. The Sonics' move to Oklahoma City is Stern's stick, and the Kings' move to Seattle could be his carrot.
That's why, if you live in any city other than New York, Boston, Chicago, or Los Angeles, this should matter to you. The NBA wants a new stadium in each city every 20-25 years, and it wants you -- the taxpayer -- to pay hundreds of millions of dollars for it. If your politicians say no, the NBA will take its ball and go play somewhere else -- and the NBA knows that's not likely to happen, because the electoral effect of losing a beloved sports team is more visceral than that of the impenetrable financial calculus of stadium subsidies.