I agree with you that Lee and Bradley are both integral to the success of this team in the short term.
That's not the only reason not to trade Lee, though. Lee is a very good value on his current contract, early-season struggles aside. We have him locked up for the next few seasons. Why give him up just to get another role player at PF?
At best, that's a "win now" move -- which is not the kind of move this team should make, winning streak or not.
Unless we're getting a long term fixture in the frontcourt in return -- e.g. a Marcin Gortat type -- I don't see the point of trading Lee this season.