Why is Boston supposed to be worried about 5 years down the line?
Because the most important thing in attracting free agents is a culture of winning. Having players on your team who are reasonably young, but still playoff-veterans, while maintaining a winning environment is exactly what you need to get a player like a Chris Paul or a Carmelo Anthony to bolt his team in favor of yours.
In my opinion, Rasheed Wallace does not put Boston any closer to a ring than the continued development of Davis and Powe does. Now if we're talkiing that Boston were picking up a player who is arguably top 5 at his position to play behind one of my youngsters - like an older Jason Kidd - then I regard that as a good thing, but when it's a player who is going to take time away from your developing youngs, that's a problem. And if it's a player who puts you over the top, I can agree (signing of both Payton and Malone by the Lakers, for example).
Now the idea of a "youth movement" - such as trading Garnett for Amare Stoudemire - *THAT*, I'm against. That's sacrificing the present for the future, and it's why teams like Minnesota remain teams like Minnesota. And you don't trade away "cornerstone of the franchise" players just because they get old, either (like if San An had traded David Robinson his last year, or the Lakers had traded away Kareem or Magic in their last years). And dumping players for savings? Kiss of death. Phoenix selling draft picks and dumping players for cash qualifies, but so does Dallas dumping Michael Finley for luxury tax savings (anyone think Dallas would have collapsed as badly as they did in 2006 had Finley been there instead of Stackhouse?).
The message you want to send a superstar is this: You want to play here, because 1) you'll win - just like we have for years, 2) you know what our organization is about, because we're never in constant upheaval, 3) we're looking to both right now and to the future, 4) you'll be loved and cherished by the community and the franchise until you decide you're done, and 5) the money is here right now and in the future - we'll spend to win if that's what it takes, rather than asking you to take a pay-cut to help us "remain competitive."
But back to the original point - by building up young assests, you've got sign-and-trade potential for the "second" superstar - the one you won't have the cap space to sign out-right.
Rasheed doesn't really enhance "win now," and he hurts "win 5 years from now." That's why I consider his signing a mistake for Boston.