Avery's probably slightly overpaid, relatively speaking, but it's not that bad. He's the 98th highest paid player in the league, and he's surely not in the top 100 among NBA players, but he's probably close to being in the top 150.
As someone above mentioned, he's a good role player, a lunchpail and hard hat type glue guy--the kind of player every team loves to have. Not a star, but a competitive role player with a defined role.
All in all, I'm not going to quibble over the fact that he might be 1 to 2 million dollars overpaid. I like Avery and I'm happy with his contract.