it's really cool that you get excited enough to post it up here when you find 'em
I think that the uniqueness about collecting coins and paper money is the excitement it generates. I have some specific interests with respect to coins and banknotes and when I share that with other people they invariably comment on the excitement it generates. This is invaluable.
Surely if you can make money on the way that's great. I saw on e-bay that a $25 VF note sold for $5000 and a $500 note sold for $10000. Assuming the starting point of 1935 this represents a rate of return of about 7.5% annualized on the $25 and about 4% annualized on $500 notes respectively.
Compare that to an average return of around 9% annualized for S&P over a 25 year period.
Other than short term opportunistic motivation for making money and I think collectors have to see beyond the investment potential.