Don't sign me up.
Again, as good as CP3 is, what has he proven? Nothing.
The current Celtics team has proven that when healthy, they're easily the best team in basketball. If they actually replenish the bench they had two years ago and accompany that with the upgrades the have in the starting lineup (improvements with Perk and Rondo, Ray fitting in better) and they have the potential to be historically good.
Is there a chance CP3 makes them even better than that? Maybe.
But I don't see why you gamble a couple of potentially epic seasons on that.