There are no facts I know of why Gavin Andresen's creditability should take any hit so far.
The fact that Gavin has said he believes this guy to be Satoshi when his false signature claim was debunked within hours shows that Gavin has lost all credibility (where is Gavin's response to the debunking?).
The evidence that Gavin (allegedly) saw was not the debunked signature. Gavin has claimed to have seen a signed message from the address that received the coinbase transaction for the block subsidy from block "1".
If this can be proven to be true then I would say that Wright is reasonably satoshi.
If it was true (that he could produce a valid signature) then why would you go to the effort of posting such a hoax on your website?
And why doesn't Gavin just post the public key and signature?
(hint - he can't)
You should perhaps be considering Occam's razor here (the simplest explanation being that Craig Wright does not have the private keys he is claiming to have).