I don't think players think about "rivalries" when choosing a team. My guess is most players believe rivalries are made by the players, not the cities.
I think these are the things they consider when choosing where to go:
1. Who can pay me the most (if its close, then they can look at other factors)
2a. Where do I want to live?
2c. How are the teammates...are they built to win?
3. How is the organization/historical impact?
Basically, if the C's have max cap space, and other teams don't, they will be in the running. But depending on what other teams have cap space, they are going to have a tough time winning the battle for these guys.
Boston is not a super attractive city to NBA players (I would say they are towards the bottom of the middle of the pack, behind the bigger markets, and warm cities, but ahead of the tiny markets, and cold ones).
The organization is good, and the history is there...but I don't think many players put a ton of stock in that. If everything was even between lets say, the C's and the Bobcats, then it might make a difference, but there is a rare situation where this will really have a bearing.
And the C's core, as it stands now, of Rondo, Perk, and Davis is not really the most attractive core out there. Rondo could be a star, but he still has a bit to go, and none of those guys have a reputation as incredibly fun teammates.