The most important thing Volchenkov brings is his physicality. His hitting is why he got a $4M contract instead of a $3M contract in UFA. I do think he's an important asset, but what it comes down to is if he isn't providing a physical element - an intimidation element - to the blue line, he isn't living up to his contract.
(His physicality and its contractual value is why DATW constantly believes he's not worth what he's getting paid, because a great physical game is worth approximately the same as a great offensive game for a defenseman on the UFA market.)
I'm okay with his contract, if he's bringing both solid defense and terrific physicality. Even in the absence of a good puck-moving game. You need at least one guy on a lineup who forwards say "I'd really rather not get hit by that guy."
As I've posted many times before, my ideal defense:
(1) Power-play Quarterback (Zidlicky, Rafalski, Niedermayer)
(2) All-round mobile defenseman (Tallinder, Greene, Niedermayer, Stevens, Albelin, Fayne etc.)
(3) All-round mobile defenseman
(4) All-round mobile defenseman
(5) Shutdown Defenseman (Salvador, Volchenkov, Stevens, White, Daneyko, Niedermayer)
(6) Physical Defenseman (Volchenkov, Stevens)
(7) Reserve Defenseman (Just be reliable, but preferably with a physical game)
You'll note that a guy like Stevens can do just about any of the roles above. That's why he's Scott Stevens.