You answered your own question.
I guess I should specify. Is all of this true regarding pick guards as well? Are they just as rare and valued, etc.? To me personally I see very little difference at all between a signed guard and the actual guitar.
In many cases an autograph on the body of the guitar can command a higher premium than one signed on the pickguard. It's just a matter of if the seller prices them right and waits for the right buyer really. In regards to someone like him or Clapton where they simply stopped signing both, there's not as much difference in pricing. People are going to pay a premium and be happy to find a rare authentic autographed guitar regardless of the signature location.
The guard is a bit of plastic signed, the guitar may never have been seen by the artist. To me is just a way to increase $. I do not like guitars signed in the guards.
signed on the body is worth more than pick guard and usually rarer.
most people never did full guitars but did pickguards