The only thing looking "under" the model can be useful for is comparing the 3d elevation of a tracklog to the DEM model -- sometimes it will be underground, so to speak. This is somewhat of an esoteric feature (I imagine most people turn the 3d tracks off since they clutter the view), but I don't think it's that hard to get back to a reasonable view if you do it accidentally. Going out of 3d mode and back in will do it, for example.
Zooming on the tilesets would be very cool. I often wish I had a more detailed (higher resolution) map on the model. This would take some serious work, however... but in the course of doing the larger-than-screen export it may be possible to at least make the texture larger to help with the problem. It's worth some more thought, at least.
