I would do absolutely nothing but wait.
Mike Miller will be a great fit to complement either/both Lebron or Wade, and if/when healthy, he'll get 30 minutes off the bench in a 3-wing rotation that will be one of the best in the league.
Bosh is still a pretty good player. He's starting to figure it out.
They have significant holes, but only need the right couple of role players to fill them: A PG that can defend the position and spot-up for 3, and another big that can rebound and block shots. There's a good chance they get better through buyout pickups (including, perhaps, even Marcus Banks). They don't need offense-oriented players (though some plays would help).
Part of the problem is they wasted two spots on the wrong complementary pieces: Juwan Howard and Magloire are the wrong pieces--they shouldn't be on the roster, let alone the floor. Better give the spots to a younger, more energetic player.
Next offseason (presuming a normal, non-CBA disrupted offseason), they'll have the MLE to fill the gaps.
They don't need to make a major move; they need to find the right complementary pieces to make this powerful engine run more efficiently.