I also have noticed a decrease in the quality of the Wilson over grip. Not enough at first to make me switch (plus I buy the 50 pack so I was stuck for a bit lol)...
But now I use the Volkl v-tac. The good part for me is the more I play with it the tackier it seems to get, but its not as durable as the Wilson. I can see little spots where I've worn out the grip a bit. Still playable but just annoying to my OCD self.
Whereas the Wilson seemed to lose its tackiness rather quickly.