le-sheq wrote:
is the leverage benefit big enough to justify extra money spent on the
longer (175) crankset?


Save your money. That 2.5mm difference is extremely tiny, and the
"benefit" even with something much longer (or shorter)might be zero.

Studies on the effect of crank length on performance have not been able
to find any meaningful correlations. Practically all riders can perform
optimally with the standard lengths, unless they are very short.

BTW, this has been discussed many times on this newsgroup... and
recently, too. Do a search if you'd like some light reading...