I did the Western Wonder back in 2004 and it was great, at first I was hesitant about where the money went but after 2-3 days on the bus I realised that what I was seeing was worth twice what I had paid. Someone asked me when I got back "Couldn't you have just hired a car and done the same trip?" The answer was absolutely not!
Maybe I was lucky to have a great bunch of people on my bus but the Trek leader (I wish I remembered his name cos I'd like to speak with him again) made everyone feel relaxed. The highlight, if I had to pick, was probably the limo down the strip in Las Vegas. Apart from that though the national parks we visited were breathtaking, I especially remember Vernal Falls in Yosemite.
Basically, if you have a week spare and you wanna get between LA and San Fran, or vice versa.. DO THIS TRIP you will not regret it!