One thing that supports what you're saying is that if Danny waits judiciously to see what kind of value they command so he doesn't overpay, I get the feeling both Garnett and Allen will see it as a slight, much like TA and Leon did.
Here's where I disagree with that. Follow me on this logic...
All the way back in 2003, Ainge was in charge and wanted to add some vet help to his team. Supposedly at 12:01am at the start of free agency (exactly one minute after teams could speak to potential free agents), Ainge knocked on Karl Malone's door. Malone was 39 years old at the time, but still effective in his previous season with Utah. Ainge offered him good money, tried to sell him on the storied Celtics tradition, and stressed that Boston could be a great fit for him. It was the ultimate show of respect for a veteran big man. Malone eventually decided to sign with the Lakers instead.
Now stick with me here. List the best unrestricted free agents in this free agent class. I got Deron Williams ranked #1 and Kevin Garnett ranked #2. Ray Allen is probably in the top 5. We are very unlikely to find a better option next year through free agency. Seems to me if Ainge was willing to give that kind of respect to 39 year old Karl Malone... he should have no problem showing his appreciation for 36 year old Kevin Garnett. I really think Ainge should probably just be up front with KG... ask him he wants... and give him whatever he needs to return. Be transparent about it. There is no sense is messing with him. As long as Paul Pierce is still under contract we don't really have any real cap room to play with (25 mil total if we let KG, Ray, Jeff Green, Bass and Pietrus walk. Can you think of a better use of 25 million??)... so just bring KG back for whatever he wants. Hopefully he will take a major discount.