I honestly don't see much of a difference between the prototype and the final product. The softening of the details and changes in paint apps is to be expected--it's the same with most of their other figures. I agree that the mustache is much much more pronounced in the final piece and makes a significant difference in the overall likeness. But I always saw problems in the likeness to begin with in the proto. That upper lip area was always a bit questionable--the mustache just accentuated it.
Anyway, I didn't buy because I never felt good about the sculpt and wasn't that enthused about the overall "look" of him in the black suit. I've got the Last Stand Wolverine and am pretty happy with him because despite the sculpt not being amazing, it's still pretty good and overall is a strong rendition of the character. He's got the hair, the angry intense look, and the X-uniform.
I agree with most that the best way to vote is with your wallet. Either don't buy him or return him. However, I think that HT and Sideshow tend to twist this around on us and claim that bad sales meant that there wasn't enough interest in the line/character and therefore will not be doing new figures. They never for one second admit that it was anything lacking on their end that caused that waning of interest.
I will say that just the action of creating the petition and hopefully getting a good amount of people to sign it may at the very least send a clear message that many were not happy with the final product.