The prisoners dilemma:
If everybody were to sell (or better use) part of their hoard over time the market would become more and more healthy as the fear of dumps depreciates. In terms of the dilemma that would be to cooperate.
Unlike in the prisoner's dilemma, you can very well use Bitcoins (i.e. cooperate in your terms) without reducing your expected reward from future price increases: by simply restocking your BTC regularly.
I happily spend, donate and trade Bitcoins all the time without my savings wallet getting touched. Unless your strategy is to hold even the last bit of your wealth in Bitcoin, there is no prisoner's dilemma here.