Love is a main man offensive type, and he's been overshadowed by James in Cleveland. Good perimeter shooter/passer, fair defensive rebounder. An upgrade over any of their 4-5s, for sure. He would be their big go to guy on offense, and maybe push IT back into the 6th man role, where many think he belongs. So he has value to the Celtics.
I wouldn't value him at the #3 level because of his salary. At this point, he is overpaid. Ainge might be interested in a deal for one or two of the lower #1 picks, and one or two players not part of their core, as suggested in an earlier post. Olynyk would be expendable.