Thornton is a gunner only. He can put up numbers in a pinch, but we already have a microwave-type scorer in Isaiah Thomas. Not to mention IT is already tied up to a cap friendly long term deal.
I would rather spend our free agent dollars on our real needs - rim protector and/or a versatile scoring SF. We will address one of these needs in the draft. I'd rather save our cap space to splurge on one bona fide FA star, then use it up on journeman/role players such as Thornton.
No offense to Thornton, but we could do better with our cap space. He's a good player for the right situation, but I don't feel at this time that he is a good fit for the Celtics.