On the one hand you say address the pass rush, just like that, minutes later you tell me why they didn't. If they weren't able to fix it because of the reasons you stated why would they all of a sudden be able to do that now?
Do you really think Belichick doesn't think a pass rush is important? Or do you think that Belichick doesn't see the pass rush as a problem? I'm betting he does think it is important and that it's lacking has been a crutch to the defense and the team. But there is not an easy way to generate a pass rush because the good 34 DEs and the good 34 OLBs are rare and thus expensive.
Asomugha is availiable and the price to sign him is unknown.
Sure, Clay Matthews might've been a solution, but he also may not have fit in here. Who knows? Maybe, BB put too much stock into Crable. So yeah, in recent years the pass rush hasn't been addressed very much, but not addressing it is better than signing another head-case FA (Thomas) or drafting say a Gholston.
Do you really believe that BB didn't make any moves because he had Crable on IR? I've tried to figure out why he doesn't pay more attention to the position but to say its because of Crable? That's a good one, as is suggesting that they draft Gholsten.
But, I don't believe in fixing the pass rush by signing a cornerback to a contract worth 30+ million in guaranteed money. Seems backwards and indirect to me. Will the best CB in the league certainly give our poor pass rushers more time to get the QB? Sure. Will our pass rushers still be poor? Yeah. I think you fix the pass rush by drafting and developing pass rushers, not by signing cornerbacks to monster contracts. (e.g. Cunningham and hopefully future draft picks).
I don't think fixing the pass rush by signing a CB is the best way either. However, for reasons you already gave, it is not easy to improve the pass rush in the front seven because "good 34 DEs and the good 34 OLBs are rare and thus expensive" As I said NA is availible and his price is unknown.
And just because the Patriots have the cap space to sign Nnamdi doesn't mean the team should. Say the Patriots have $20 million dollars in cap-space for the 2011 season. Nnamdi will certainly command $10-15 million dollars of that space. So what kind of players will the team bring in to fill the (1) offensive guard positions (2) outside linebacker (3) offensive tackle? That's four very important positions with only $5-10 million dollars of cap space dedicated to them. And don't forget three of those players are protecting the team's most valuable asset, it's $20 million dollar/season star quarterback.
Signing bonuses allow you to spread the money throughout the length of the contract. It is doubtful his salary cap # would be that high. (assuming a cap is in place). NA is a free agent, there are not a lot of options on the free agent market at OLB and a top tackle would be just as or more expensive if available.
Of course, Nnamdi is one of the best players at his position in football, and he is still in his prime. But according to the needs of this team, is he really worth 10+ million dollars a season? Is his play going to put the team over the top to get to the Super Bowl? I think not. Or will using that money elsewhere bring a greater benefit to the team? I think so.