I think a scaling detail function would be ideal (beyond meshing angles), automation of this function may be very complex, however I have seen it achieved with polygons (e.g. Torque game engine demo, this is much like the meshing angle option I suspect). Maybe a filter that looked for all surfaces below a set size (area) at each detail level, but replacing them with a different geometry (some sort of interpolation) may require more processing than display of the original. Perhaps a simple show/hide functionality, my only concern is that this approach would drive the desire to model extra (simplified) surfaces. I think this is a tough one, I cannot, off the top of my head think of a good way to do the math to achieve this on a nurbs model, especially since there are so many distinct ways of generating features on solid models these days (yay for that). But, I'm always available to bounce ideas off of. Maybe a simple elimination of vertices that are co-located within a set 'mesh' (for lack of a better theoretical term) size, but this may not give the desired result in all cases, and surfaces would be recalculated each time the 'mesh' was re-scaled.

Adam.