Okay read every word I say, every word.
The GS has no relationship to the Avalon. Unlike the ES and Camry which share a basic platform (even they only share about 20%) the GS and the Avalon share NOTHING except some filters and maybe some switchgear shared between all Toyota Lexus vehicles. They're about as similar as the Corolla and the Tacoma truck. The two cars are completely different and target completely different companies.
I sat in the new Avalon today, didn't get a chance to drive it but I will. Its very nice, but its not a Lexus. The quality and hefty build aren't the same, the controls and doors etc in the Avalon felt lighter and less damped, leather was lower quality as were plastics. Getting back in my ES there's no question which car is more expensive and more solidly built.
A lot of Lexus owners are all messed up about the Avalon, you've just got to remember that a luxury car is engineering and quality first, and look and features second. The Avalon is nice, but its no Lexus. If you're buying a car for flash and to get attention then you're in the wrong car, you need to buy a BMW or a Mercedes. I drive my Lexus because I love it and it makes me happy, I really don't care if other people like it or think its a Toyota. Doesn't bother me.