You don't always have to have a ton of money to attract guys to your club, and yet, even when the Fantastic Four were here, we were still not a primary destination. All I've ever seen is guys willing to take sometimes substantial pay cuts to sign somewhere like New York, LA, Chicago, and Miami, but that is never the case here, no matter what stage our team is in. Guys have said in the past that Boston is, "too cold," in addition to other bogus reasons for not coming here.
There were players who took substantial pay cuts to play in Boston in the KG era. Start with players like Posey, Daniels and Sheed. Also, one of Lee/Terry talked about how they turned down better offers to sign in Boston.
Not to split hairs (but totally splitting hairs ), Posey took a calculated risk because his value around the league was low at the time. When he showed he can still give awesome hugs and hit the occasional 3pter he might as well have had a jet pack on his back to get out of town.
Sheed as well, maybe a little paycut, but nothing approaching anywhere near the level Ray Allen took to play with Miami over a much more substantial offer from Boston.
There have been some undeniable coupes (at the time, which is what matters) during Boston's title run and almost title, as well as after, but they weren't all wins, and I don't think we could extrapolate those victories into proof positive of anything, anymore than the Celtics lack of ever landing a 'big fish' in free agency because they have never tried is proof positive that they cannot. The two arguments fall victim to the same flaws.
Plus, how many of those top-tier in-their-prime guys leave their teams anyway? It's pretty rare, although, obviously, each situation is different. Tim Duncan almost left for the Magic, but that's about it in terms of franchise guys from 1996 onward. Dirk, Pierce, and Kobe never left, and Garnett had to be convinced to come here. The whole Miami Heat phenomena was to free agency what the KG and Ray Allen deals were to trades - it was an extremely rare, once in a generation move that occurred only when all of the stars perfectly aligned. Free agency isn't like playing a video game, as much as we'd all like it to be at times, haha, because the guys who are the best of the best are hardly moved, especially in their respective primes, and, unfortunately, Boston has just never been a marquee destination for those types of players. Perhaps it's all driven by marketing and other business potential crap, which is another reason why guys want to play in New York, Chicago, LA, and now Miami - the exposure, the endorsements, etc. Guys like Paul Pierce, Joe Johnson, and Michael Redd are/were some of the best players of their generation, and yet they have pretty much always flown under the radar because they're not in commercials like Wade, Kobe, Lebron, Jordan, or Shaq. The first time I ever saw an endorsement for Paul Pierce it wasn't even a commercial - it was an ad in a magazine for Backyard Basketball or something lol. Now, is that because of Boston, Milwaukee, and Atlanta? I honestly don't know, but it's clearly not the same as playing for LA, New York, or Chicago. Boston is the classic small market team, quite honestly, in the NBA, which is hilarious when you consider the history of the franchise.