The Bass/Howard didn't work out too well in Orlando, if I remember correctly.
I like Bass here, I think this Celtic team is in position to sneak into the playoffs and I think Bass helps. Why give up a solid vet PF with an expiring for cap relief and mid-level prospects? We will have a more than enough prospects coming through in the next couple years with all the draft picks. I say hold onto Bass and other expiring contracts in case a superstar around the league wants out. Boston's expiring contracts combined with draft picks could facilitate something much bigger. At worst, like I said, we have a vet PF who can help and that's expiring.
Edit - I didn't read the article until after my post. I think more minute allocation for Zeller would be a good thing. Bass is a big boy, he can handle getting paid almost $7 million this season in very limited use. I still say keep him here.