First of all, Ray Allen is merely a catch and shoot player these days, because that is what the offense the Boston runs ask of him, and he sacrificed his game and adjusted his game to fit the Boston offense when he was traded to the celtics.
Ray Allen was getting most of the offensive touches in Seattle, you dont go from avg. 26 ppg to 17 the next year, without some major incident happening.(the trade and then sacrificing)
Anyway, Ray Allen is the oldest of the Big 3, but he seems to be the healthiest. If you think about it he's been the healthiest player on the entire roster this year.
I wouldn't trade Ray right now, bc of course we are still contenders,and I wouldn't risk ruining the chemistry that we currently have. Getting young guys in the middle of the season, you run the high risk, of them not understanding or picking up the offense, not understanding how the C's like to play defense.
I dont think it would be smart to use the season, as a training camp for anybody during a championship caliber season.
Also, I wouldn't want to trade Ray Allen away, because there's a chance Ray would be willing to re-sign for a lot less, than some people would expect.