I would be in favor of signing Bynum as I do think it's worth the gamble.
However, to me, it would make no sense to sign Bynum and use him as part of a rebuild.
If you sign arguably the 2nd or 3rd best center in the league, you should be competing, not signing him and then telling him to take his sweet time coming back.
It's like me buying a nice, shiny new car but having to wait 9 months to drive it.
I ain't waiting, I am driving that [dang] car now (lol)