Thoughts behind future classics and the beginning to this series HERE.
Over 12,000 E34 M5 were produced during a six year production run. A rare M5 then can only be found in the special editions. Luckily there were three very limited production run special editions of the E34 M5 built. These are the Winkelhoek Edition (51 built), Cecotto Edition (22 built) and 20 Jahre Motorsport Edition (20 built). They are all special in their own way and equipped with the 340 hp 3.8 litre naturally aspirated inline six.
Avus Blue E34 M5, photocredits to: https://www.flickr.com/photos/connorgt3
If you can't find any of these unicorns, you can always search for the E34 M5 Touring. It is the second rarest regular production M sport BMW with only 891 specimens made. With the first (E28) M5 and M535i already a classic, the E34 will certainly only go up in value. Remember to go for the 3.8 litre straight six though because it has some extra tech and the added horsepower. The ones built after May 1994 even had six-speed manuals.
If you want to add value to your E34 M5 and why wouldn't you, you should search for an M5 with the Nürburgring package. With the Nürburgring package you got wider wheels and tyres and the, then high tech, M adaptive suspension.