I didn't think he was worth more than $7 mil/year, either. Danny made him a fair offer in what he honestly believed Perkins' top market value was worth (at least in the case of the Boston Celtics' perspective). Tough to see a fan favorite go, but it was the right move. With his string of injuries and prior surgical procedures, that $9-10 million a year mark was a bit too high.
This certainly was not a case where you go the extra mile for one of your guys and overpay him out of respect. Perk was a vital part of the team, but he wasn't one of the "main, main, main" guys. The Celtics believed he had good talent, but that it certainly wasn't irreplaceable. Danny has made it known for years that he listens to all inquiries and "kicks the tires around" with all players on the roster, nobody is safe from being traded. He needed to fill a void in the roster at the 3, traded a vital part of the team, but got back his 3, as well as another 5, whom thus far has exceeded expectations and is making everyone deal with the trading of Perk just a little bit easier.
I wish nothing but the best for Perkins. He was a big part of the '08 title team, and was probably the missing link in last year's game 7, though we can never know 100%. However, basketball is a business, just like your local 7-Eleven is a business. You reward your employees with raises as you see fit, only on rare occasions overpaying if you honestly need to, because you really can't or don't want to lose that piece. Whether it's out of respect or any other reason, you overpay rarely. Business is black and white and you can't let those shades of gray get in the middle when it comes down to the dollar and product you are trying to put out there, and that's what Danny was doing when he pulled the trigger on the trade.