If Philly makes the Lakers' pick available, then any trade you're making is primarily for that pick and Noel is almost filler. He's a useful defensive roleplayer, but he's getting paid next summer, at a time when Boston has their sights set on better players. I'm not giving up Brown for a non-star who might walk in a year, especially when there don't appear to be any (any other?) serious bidders for Noel, when Boston's the team in much better position to wait out the other.
EDIT: Also, the Lakers' pick is probably a toss-up to convey next year, as there's a decent chance they're the worst team in the West again, but that's not necessarily the worst thing, as this team could stand to continue to roll draft assets forward. Getting the 4th/5th pick in next years' draft would be ideal, but having the pick not convey would be okay too. To be clear, I don't think Philly makes it available in any trade the Celtics would consider.