I'd like Vince on this team. I'd like the chances of one of Ray/Pierce/Vince going off for a vintage game every playoff game; I think our offense would be more potent. A Pierce and Vince wing tandem especially could allow the Celtics to be more unpredictable offensively.
That said, he'd be worse than useless in year 2 of the deal if Ray and KG retired, just clogging the cap.