I'll freely concede that I may irrationally like the guys we have, but I'd rather see what they can do. Even if we got Kearse, I don't see him as any higher than WR4 on this roster, and he's likely not even that.
Kearse is a better WR than Carr, but considering that the WR5 role would likely be more ST than actual receiving and the disparities in pay and age I'm not sure Belichick would consider it an upgrade worth giving up any asset for.
I expect WR5 to come down to who can better cover kicks and return punts.