Well I started this thread and I wouldn't do it. Even if 100% healthy, Arenas would take away all of their financial flexibility for at least 4 years. Plus they'd have half of their cap invested in two small backcourt players, assuming they resign Rondo.
Also, Ray's expiring deal gives you flexibility at the deadline. If Charlotte's or New Orleans' season goes into the toilet (either might happen) you could get a very good package for Ray, including draft picks to help reload after KG and Pierce retire.
If Washington offered an unprotected first rounder along with Arenas, I would reconsider. There would need to be a major sweetner like that to induce the Celtics to take on all of that salary.