The key is the draft picks and expiring contracts that is how you get players in sign and trades. I agree if a free agent was going to be knocking down the door to play with Rondo wouldn't they have done it when we had Rondo, PP and KG?
First of all, welcome aboard. That said, I don't agree with your statement.
The key are not draft picks and expiring contracts. The key is getting value and keeping flexibility.
The picks we would be getting back for Rondo are not that valuable. The Detroit pick, as Chris said, might not be in the lottery. The Dallas pick is a long shot, because the Mavs owe their first round pick to OKC (it's been mentioned in the bring back Perk threads) and it's top 20 protected until 2018, when it's unprotected.
Sending Rondo, Courtney Lee, Melo and Jordan Crawford to get rid of Wallace's contract seems a bit too much. Yes, you're clearing a lot of money, but you end up like Cleveland before getting Kyrie, or like the Bobcats. Not a good plan.
What the Celtics need is keep their own assets, and only trade them for better ones. If you have to give valuable pieces to get rid of Wallace, you better keep him and try to find a better timing for the trade, maybe he can rebuild his value playing well for the Cs.
Melo is a project, develop him and maybe in a year or two he can contribute or be useful as a trade chip. Courtney Lee can be traded for something useful right now, why dumping him as salary filler?
Getting rid of bad contracts is high priority, but you don't need to rush it. Right now the Cs need to do something with Randolph before his contract becomes guaranteed, and they should be looking to send Humphries for a TPE and a second round pick. If any trade involving Lee and/or Bass can bring TPEs/picks/young players, you do it in a second. But you don't send your best player for cap relief and a couple uncertain picks.
By the way, Cuban makes out like a bandit in this trade scenario.