Either you can run MeshToNurb on the imported mesh, or, normally, with the Sketchup to Rhino importer, you have the option to create Rhino surfaces on import insead of meshes.
One way or the other, once you have polysurfaces, I would then run MergeAllFaces on the them- do this in small batches if there are many objects.
Thanks, that did it. The only wired thing is that the display color defaults to black (white in 3d view) so I have to set everything back to “by Layer” after import.