Given what even mediocre centers make in this league, if Perk is only going to command 8 million or so a year, he's a bargain.
Is he mediocre on offense? Sure, but he's serviceable. And as far as defense is concerned, he may be the best defensive center in the league not named Duncan or Howard. Might Camby and Chandler block more shots? Sure, but neither are physical enough to challenge guys like Howard.
A guy who is a dominant defensive presence in the middle isn't something you look to trade.
I hear what you're saying, however...
There is only one guy like Dwight Howard. One. We don't need him against the other 28 teams. I think his value in defending Howard is true, but there's only one of him. And his teammates don't get him the ball. If we keep him primarily out of fear of Dwight Howard, that's not a smart move.
And you mention the guys getting more blocks. It's because of their excellent help-side defense. Perk is good, and above average, but his not dominant in that way because of his limited athleticism.
So on balance, saying he's a dominant defensive presence means valuing post defense (needed against one guy, sometimes) more than help-side defense/shot blocking (protecting the rim from all of those excellent drive to the hoop players that blow past Rondo, Ray, et. al.). I can't go with you on that. He's certainly a top defender, but not a dominant defensive presence.
His trade value probably exceeds his real value, but I think his real value is overstated. It would probably be worth shopping him. I'd take one of those other, "lesser" shot-blocking centers (who are all better offensively due to better mobility/hands) and a nice high draft pick in a second.
I hear you to an extent. I think the NBA was partly ruined by teams trying to draft "Shaq stoppers" in the '90s. Consequently teams wasted draft picks on talentless 7-0 300 lbs oafs like Todd Fuller and Sagana Diop hoping that the select few games a year they played Shaq, they'd help. Consequently, they hurt the team other games and certainly made Shaq's job easy on the defensive end, as they posed no threat to score.
However, Perk's not one of those guys.
In today's league, even with deflation, 8 million dollars is the going rate for a starting center, and actually a bargain for, at a minimum, one of the top 10 centers in the league.
It'd be one thing is he was a shooting guard, small forward, or even a power forward, but centers are rare commodities. Outside of some G.M. doing some crack and trading some up and coming star for him, I don't see how we'll ever get equal value.
And while I don't think Perk's value is solely in guarding Howard, we need to remember that Dwight is still very young and will be around a very long time. If we hope to continue to contend for the next couple year and beyond, we may see a lot of him in the playoffs. Having someone like Perk shouldn't be underrated.