I'm on the record as saying I don't see the Celtics being able to sign any top young free agents this summer. There just aren't a lot of promising young players who are in bad situations or on teams that can't figure out ways to fit them reasonably onto the books. Old free agents I'm just ignoring because they wouldn't fit with this team's current age and they care more about winning than money at this point of their careers.
I do agree with the point, however, that it's all about getting value for the money spent. Is Avery Bradley that much better than someone making 3 million? 5 million? Does he have a chance of playing better than his deal? What about the odds of regressing? Is he tradeable tomorrow if you tried to deal him for nothing in return? I can't say right now that he could be and that makes it a bad deal in my eyes. Not a horrendous deal but just because we can afford it doesn't make it acceptable.
I think Ainge will try to get one of the top RFA that are still young but will be rebuffed. Then he will go for some of the bargains a la Evan Turner last year to maintain flexibility. Next season will be another losing season though you have to assume they will be better than bottom 7-8 range just due to the extra experience gained. After that you hope that the guys you have drafted have started to make enough progress to make the team competitive enough to make the playoffs.
Some things that would delay the rebuild are not getting a major hit with their pick this year and not finding a defensive big man. If they go another season not accomplishing either they will kind of be in the same situation as Orlando - lots of nice players but no real stars after a few years of rebuilding (though Payton has the potential to be very good).
Rohrbach made a good point in his recent WEEI column
http://www.weei.com/sports/boston/basketball/celtics/ben-rohrbach/2015/01/12/danny-ainge-sets-sail-uncharted-cs that really, since the Rondo pick Ainge has not had that home run, no-doubt-about-it pick. We've had some nice surprises here or there but nobody that is special or all-star caliber. Yes, he hasn't always been picking in the best slot but it didn't stop him in the past with the great Jefferson (15th) and Rondo (21st) picks. Is it being too harsh to expect better draft results from Ainge considering where he's been picking? Maybe, but that's also what it takes to be competitive in this league if you're not bottoming out like the Sixers and picking in the top 5 every year. There ARE lots of very good players taken outside the top ten and at some point Ainge is gonna have to hit big on one of those.
BTW, I like James Young so maybe that's one of those big hits

. Nurkic would have been even more awesome but hey, he went before our pick and maybe we had no shot at him.