The Road Star motor is a single pin crank v-twin: It's gonna vibrate a bit. Without seeing just how much the bike you saw running was shaking makes it difficult to say if it's excessive or not. Curious as to what year the bike was.
I own a '04 1700 and if I'd known a bit more about the difference in the 16 00/1700 bikes I would have been looking for an '05 or newer model. Several reasons for this. A couple are: More robust charging/electrical system on the later models and the possibility of
SVS being less in the newer ones.
That said, I have had nothing but great performance and durability out of my ride. It doesn't leak, smoke or sputter(well, a little if I goose the throttle). The bike runs strong and the vibration smooths out considerably at highway speeds.
Do the maintenance as you should and you'll get many, MANY miles out of a Road Star. I've heard of more than a few bikes going well over 100K miles with no major rebuilds. A huge plus for most folks is the large amount of aftermarket parts out there so you can trick it out or alter it to make it exactly what you want it to be.
I'm sure others will chime in, but now you've got a starting place with my .02!
-M7