There are a bunch of 'rare' pre war bikes. unfortunately about 90% of those aren't worth a lot of money e.g. first year girls Huffman ballooner. The rare and desirable bikes are the ones most collectors know e.g. Blue Bird, Speedline, Aerocycle, etc.... V/r Shawn
I find some of these "rare" bikes are "rare" only because they were just fugly and nobody bought them back in the day....Evinrude cough cough... bowden .. cough gag.. ok I think I got it all out...I know last one is not prewar .. cough
How about the Alexander Rocket?
It could be called ugly as Jason sez, but I think it's beautiful, and there aren't many around...less than each of: Bluebird 1 & 2, Aerocycle, and Speedline?
I've never cared for the Aerocycle: I see a streamlined tank attached to an angular motorbike.
For me, CF is increased by rarity, not mass-appeal.