Grey market versions of the E21 were very popular "back in the day". The 320i (the only version of the E21 officially offered in the US) was a big seller for BMW. It looked good and handled very well. However, it was not incredibly fast. The 2.0 liter (later 1.8 liter) 4 cylinder engine we got here in the US put out just over 100 HP.
The European 323i's 2.3 liter 6 cylinder engine put out 143 HP. Combine that with the lighter Euro bumpers and better brakes and it's easy to see why many people chose to purchase a grey market E21.
The seller has logged a ton of miles in this car. He's spent a lot of time keeping it in great condition. The list of work he's done to this car is very, very impressive. Given its age and scarcity, many people would only use this as a weekend / show car. You have to respect this guy for putting the kind of miles he did on this car. (And for the amount of work he did to it.)
The grey market was tainted by a few - headline grabbing - unscrupulous dealers who did slipshod work. That, combined with the complete lack of factory support for grey market cars, have kept prices of older grey market cars low. This car is being offered at just $4900.00, which is a bargain in my eyes. 
Located in Rockville, MD, click here to see the Craigslist ad.