The job of the second unit is to maintain or expand the lead. With Nate's poor offensive production, he is worthless to us. Worse, he is a liability. If he were producing offensively to offset his defensive shortcomings, then it's a wash and that's OK for the second unit (maintaining the lead), but he isn't.
As Chris alluded to above, as a 10th man, situational-type player, he is great. As part of the regular rotation, not so much.
I agree that if we can turn him and our other few meager tradeable assets into a decent sized wing, let's do it.