The chief advantage to the longer tonearm is that it has a "shallower" tangential (i.e., tracking) arc than a shorter arm. The ideal way for a tonearm/cartridge combo to play an LP is linear tracking -- a straight line from the edge of the LP to the center hole (this replicates the path of the cutting head used for making the "mother" copy of the LP). Cartridges mounted on a shorter tonearm will have a sharper arc in the path they trace than a longer tonearm.
From a geometry perspective, an infinitely long tonearm would have almost no tangential tracing distortion, but since there are obvious practical limitations to length, most audiophile arms have been 12" or less. If your turntable plinth is large enough to allow use of the 12" tonearm, the longer arm may provide less tracing distortion, and therefore better sound, than the shorter arm. I don't know that "nostalgia" plays much role in some audiophiles preferring longer tonearms, and the prevalence of shorter tonearms today may be due mainly to the smaller "footprint" of today's turntable designs.
From a geometry perspective, an infinitely long tonearm would have almost no tangential tracing distortion, but since there are obvious practical limitations to length, most audiophile arms have been 12" or less. If your turntable plinth is large enough to allow use of the 12" tonearm, the longer arm may provide less tracing distortion, and therefore better sound, than the shorter arm. I don't know that "nostalgia" plays much role in some audiophiles preferring longer tonearms, and the prevalence of shorter tonearms today may be due mainly to the smaller "footprint" of today's turntable designs.