I think the Celtics should make a play for Vucevic if the price is right. Everyone is concerned with cap space, but the Celtics can make moves to shed the difference either at the deadline, or in the offseason (Avery Bradley & Olnyk for example).
The cost for him is the question. I wouldn't trade either Brooklyn pick, or JB for him. I don't think I'd move Smart either. I highly doubt Orlando is taking Zeller, waiver wire fodder, and a pair of useless 2nds. I'd love it if they would, but that's insanity. If the price is somewhere inside, or a combo of: Bradley, some cap fillers, a Memphis/Clipp/C's 1st, the rights to Yabu (I prefer to keep Zizic), etc. then it's totally worth exploring.
My guess is Bradley, Yabu and a 1st is on the high end, and Zeller + a 1st is on the low end. Other icing not withstanding. Orlando is not looking to shed salary for a $12ish million dollar double double big man in his 20s. Not in an era where Steve Adams gets $100 million over 4 years. Orlando wants real pieces and picks in return.
Another thing to consider in any potential Celtics trade, is that they will most likely have to move a guard. Especially if they're keeping the Brooklyn pick. What's Bradley going to ask for after next season? Do you really want to pay him $20-25 million per? I think the Celtics will look to move him now. Especially since they seem to be doing well enough without him.