I wouldn't trade Rondo for any pick outside of #1, Anthony Davis. If somehow the C's could land Howard for a Rondo plus package, I'd do it. When you have a chance to get an MVP level center, you have to do it and hope you can resign him.
If someone is willing to trade a top 5-7 pick to Boston for Pierce. You'd have to take that deal. Pierce only has a year or 2 left in him. It would hurt to lose him, but the players available in the 5-7 range would be very tempting.
As for swapping the 21, 22 and say Johnson for a number 10 pick, I think I'd rather hold the current picks. The star prospects drop off after 7 or 8. The guys in the 9-24 range look like rotation players without all star potential.
If you can crack the top 7 with a package of Bradley, 21, 22, I would do that. The top 7 guys look really solid.