Rondo "only" makes 13 million next season, so this wonderful cap space that is a supposed benefit of him leaving is not considerable. I mean, Avery Bradley is now an 8 million/year player!
Cap space can increase flexibility but the Celtics are not close to contending and will not be a FA destination anytime soon. That means you either spend that precious space on an overpay for a midtier star or you re-sign your own guys. The Sixers have all the cap space in the world but guess what? They can only offer LeBron the same exact salary as the other 29 teams vying for his services. And all those rookies you drafted will be asking for raises in four years.
Also, cap space was valuable when every team was up to the cap and expirings were gold. Now a lot of teams are more disciplined and cap space isn't a rarity. This means every summer you're competing with a lots of teams who also have space trying to sign a marquee guy but probably settling for a mediocre star, or just not spending the money at all.
i understand your points and agree to a degree, but have a few points to raise.
my addition would be to say that we need to look at the $13 million NOT in isolation, but with the context of the other salaries that disappear. when done that way, the celtics have a sizeble opening for free agents, etc. that was part of my earlier post, so let's be fair.
second, on your sixers comment, i know you do not mean to say that cap space has zero value for a team. so please let me know exactly what do you mean? obviously the value is not the straw figure of "they can sign anyone and everyone" but it is just as obviously not "they wont sign anyone regardless of the cap space." i would like to better understand where and why you are drawing the line on the value of this cap space to the celtics. thanks.
final point on your final point, if the free agent game is played now as you describe, then wouldnt a large level of cap space be essential to play in that game? thus, the celtics need such space to compete in the world you lay out.