Leica's took a serious dip in value a few years ago so my M3 and Summicron halved in value, same for my IIIa and Elmar & Summar. However since the start of this thread back in 2006 the market has bounced back and is now back above the level before the market fell.

A good Leica M series or late II/III series F or G is likely to be a good investment as well as an outstanding performer. Post WWII optics are way ahead of the earlier lenses.