Well, it isn't about how many picks and players Portland would want for Aldridge.
It is about how many picks and players Portland would want for facilitating a Sign & Trade deal.
They don't own Aldridge any more. He is a free agent. If he wants to sign with the Celtics, we COULD sign him outright as a FA and Portland would get nothing.
But that's not the ideal situation for either the Celtics or the TrailBlazers. For the Celtics to sign him with cap space, they'd have to renounce all their TPEs (Rondo & Prince) and the rights to their major FAs (Bass & Jerebko). It would be much better to not do that, since those things could be useful. And for Portland, if that happened, they get nothing for him.
It would work better for both teams to do a sign & trade deal. But all you are paying Portland for in that deal is for the service of doing that. You aren't paying them the value of Aldridge.
Ideally, it would work best if Danny could find a third team with a player (on contract or FA able to be S&T'ed) making on the order of 10-12M that Portland wanted. Danny could absorb that salary with the Rondo TPE and then turn around and send him to Portland to match most of LMA's salary. He would need to provide some modest pick compensation to the third team and to Portland and one or two cheap players like Chris Babb would end up getting shuffled to balance things.
Alternatively, he could use Gerald Wallace' contract to match most of LMA's salary. But because that would cost Portland 10M that they'd have to absorb, he'd have to give them something better than a late 2nd round pick. Probably the 2015 #33 or the 2016 CLE pick would be good enough, though. We took on 3 years of his contract for a mid-level 1st. They would only be eating 1 year of it. Again, from that point, you just balance out the deal with cheap players and 2nd round picks (current or future). Wallace is a former 'Blazer so there is a small bit of homecoming there.
If you did use the Wallace contract then, as you noted, you could use the Rondo TPE to absorb Matthews, also in a s&t transaction, probably again, for a pretty modest pick.
There are lots of variations. Danny is as good as anybody at understanding the CBA rules and how to creative construct a trade.
The first step is convincing Aldridge (or Monroe or Leonard or whomever) to sign here. Once that happens, Danny has the tools to make it happen to his best advantage.