I found it easier not to use IBL. And it works for P5/P6.
Aren't you this guy called "Nodemaster"? :)
Perhaps a set of nodes for spotlight is something to get a bit more "reality" out of Poser.

The highlight problem can only be fixed with setting a parameter according to the environment, I think. Maybe a Python Dialog with some options asking for light-type, environment and things like this?

In real, each white wall in a room actually is more or less a light-emitter (think of a reflector used outdoor to lighten shadows). In my studio I use softboxes (beside of reflectors) for a similar reason.  Not sure how you want to manage this whithout GI in Poser.

By the way: Many images taken in a studio looks similar to Poser images. Because in a studio is nothing that inks the flash-light (walls are black). Very similar to Poser :). Filters (in front of the flash-light for scattered-light and/or colored light) are often used to avoid this (and to get lots of other effects).

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