Anyone who thinks Andy's artistry is wasted on clay needs to rewatch his match against Gasquet at RG again.
He just seems to lack the confidence on this surface to ever really play his best stuff. Probably down to the movement, as his confidence stems heavily from how well he's moving.
To be fair I stand corrected. That was a great match to watch. I thoroughly enjoyed it, which is not unheard of for me for a match on clay, but fairly unusual. I just don't like the clay as a surface really.
I'm convinced that for Andy it is a confidence issue more than anything. I think you're spot on about the movement. I also sometimes think that Andy needs just one big win on the clay, a win over someone people might think he'd lose to, to make him realise that he can play on it. I mean, I know I say often that I think 2011 might be a red herring, but that year Andy did take matches very close against Djokovic and Nadal. In my book that means that he can play on it at the top level, he just needs to consistently believe he can.