nothing has a definitive value, even gold. a few years ago gold was 900 an ounce, and through a series of clever marketing ploys involving scare tactics and the phase "plus gold has never been worth nothing" gold speculators drove the price to almost 2000 an ounce, now less than a year later it's only just over 1200 an ounce.
think about that, gold can only be formed in the core of a super nova star, right before it explodes, it is not produced naturally on earth, and cannot be synthesized. yet someone who invested in gold this time last year saw their value drop 40%.
yet somehow you expect a loose complete sample of a 30 year old plastic toy (subject to degradation, and declining consumer interest- proof is in the fact that modern joes leapfrogged vintage joes right here in the forums- and massive influxes of alternative parts) to hold or increase in value? hundreds of thousands of these figures were made, there's only so much gold in the whole earth, how do you expect gi joe to fend off gold's fate?