like other people have said, we can all give you our opinions, but they may not have relevance to you.
if you're doing your own research you'll see that Sun Valley is the name of the resort itself, located near the town of Ketchum. so you'll find more info if you use the town names, not the resort name.
i agree, ketchum is expensive, there is the "posh" element, and there is a sizable second-home owner population there. however, you don't need to be a millionaire to live in the area, especially if you are not looking to buy. there are a few towns down the valley from Sun Valley resort that are more working class, and not nearly as expensive: hailey, bellevue, carey, etc. i know lots of regular working class folks who live in these tows and own good homes. they are not millionaires.
i would choose the Wood River Valley in a heartbeat over CdA, and i did!
i am moving my family to hailey very soon. i think the nature in the whole Wood River Valley is outstanding, and to me, superior to that of CdA. plus you have the Sawtooths, and the Frank Church Wilderness area right there (the largest roadless wilderness area in the lower 48.)
these places have a very different feel to them. the wood river valley has a number of small towns, with a small town feel. hailey surely has strong liberal undertones, and there is a substantial ecological/environmental consiousness running through the town's population and local government.
i've found this local paper to be a valuable resource. gives you a good feel of the area i think.
Idaho Mountain Express: Wednesday - April 16, 2008