Steve,
> I've spoken with some of the top acousticians on the planet and the idea of too much bass trapping not only happens, its common. <
Yes, I've heard some people say this, but they're wrong. Regardless of how "top" they may be.
> Too much bass trapping often finds a drop starting at 250Hz <
As you add more and more bass trapping the response becomes progressively flatter and the ringing progressively shorter. Peaks continue to come down in level, and nulls continue to come up. By the time you have 100 percent surface coverage the response is finally flat. Of course, by then there's too much absorption at mid and high frequencies. Again, it's the balance between absorption at low frequencies and everywhere else that can be "tuned." But it's not possible to have too much absorption below about 300 Hz. Unless you prefer a skewed LF response with a little ringing thrown in for good measure.
--Ethan