Played around a bit, unfortunately no such "luck" as just a sloppy mesh. There isn't a single loose vertex in the whole thing... before export. If I run it "remove loose vertices" from shipEdit on the exported mesh, it finds thousands. So definitely something wonky with the export there.
The suggestion from MaxBuzz seems to help, though: If I export each object, which would previously form a mesh group, into their own meshes instead, all but the most complex ones load fine in orbiter. Looks like I have to split up the more complex one some more, which means fooling around with selection modifiers some. And then of course there's the process of selecting each object individually and starting its export and renaming the output file. It appears to be a workable solution, but as mentioned kills any semblance of efficiency. Oh well, I guess I shouldn't complain about that as long as it works...
The suggestion from MaxBuzz seems to help, though: If I export each object, which would previously form a mesh group, into their own meshes instead, all but the most complex ones load fine in orbiter. Looks like I have to split up the more complex one some more, which means fooling around with selection modifiers some. And then of course there's the process of selecting each object individually and starting its export and renaming the output file. It appears to be a workable solution, but as mentioned kills any semblance of efficiency. Oh well, I guess I shouldn't complain about that as long as it works...