In my opinion Zeller needs and deserves more minutes. Not because he is an extraordinary talent, I think with more confidence, and a bit more physicality, he could be a decent starter/backup in the future.
I happen to like Bass, I see him as a nice piece on a contender. He scores well, that 15-18 foot jumper is money in the bank. But, to sign him to new contract at this stage of the teams development is foolish. He most likely will be gone at the trade deadline. But to get something for him he has to play a little.
Zeller should get more of his minutes in the rotation. Honestly, I like Zeller as the starting center, with KO, and with Sully coming of the bench.