I propose a trade of Rondo, Green, and a pick or two (not including the Cs' own 2014 first) in exchange for Drummond and the Stuckey/Villanueva expirings.
Alternatively, if the Pistons are committed to a Drummond/Monroe frontcourt and are desperate to get rid of Smith, I would trade G. Wallace and Bogans (expiring) for him. Detroit would save some money as Smith's deal is one year longer than Wallace's. If I'm the Celtics, I'd pay the difference to see if Sully/Smith can co-exist.
Are you really serious? Wallace has ZERO Value. That trade wouldn't even be laughed at. You would be drug tested as a GM for even offfering it.
You are, of course, quite correct. Wallace's contract is an albatross. It has negative value.
Do you know who else is an albatross? Josh Smith. And his contract is one year longer and $24 million more expensive.
That being said, there is a greater chance that Smith, in a new situation, can reclaim some value (which is why the Celtics would make the trade). For that reason, the Celtics would probably need to add a late first round pick for the Pistons to consider it.
If the Pistons are committed to a Monroe/Drummond frontcourt (the premise of my trade proposal), it's looking more and more like they will need to get rid of Smith. And that's not going to be easy for them.