Is it uncommon vintage gear? Yes, indeed--there's not much that escaped the scrap pile. Office automation equipment in general is pretty rare, particularly old word processors (e.g. Artec, Lanier, CPT and others), mostly because companies elected to scrap the stuff rather than try to resell it.
Is it collectable? That's harder to say--and I'd be the last to say, since I'm not a collector--it's definitely an underpopulated category, which may make it harder to collect. For what it's worth, I believe that your system could run MS-DOS just fine, but I don't recall if it took a special version, but that should be easy to determine.
That coax connector on the back was NBI's own OASys proprietary networking system, but I recall that you can get adapters to a standard 10BaseT connection.
I wouldn't junk it--it deserves to be preserved.