If not, what incentive is there for those earlier adopters to monetise it?
It is self interest that drives everything in a market. Without that, there would be no bitcoin.
Well, if there was only that, there would be no bitcoin either.
I'm interested in Bitcoin because of the P2P monetary system experiment. I don't care about mining or speculating, and I think too much emphasis is put on mining.
In 5 years from now, we'll all be considered early adopters. Disrupting the way banksters create money and the ability to wire funds without relying on a trusted third party is enough an incentive for many.