There's a fundamental floor of value where "in the bad old days" I once bought a specialty swiss army knife (a very custom gift; details utterly irrelevant) and I wanted the knife enough to pay middlemen about 20% overall to turn by USD into ... whatever the swiss were using at the time. It used to cost twice as much money to move money around the world than to move a small consumer good around the world. That's just how the world was. Weird to think it would have been half the cost to mail the swiss a gold coin than to transfer money all legally.
Clearly, I didn't think the middlemen provided 20% of value, but I was willing to cough up the cash to perform the overall transaction. If a cheaper money transfer option existed I'd never have used the middlemen, whom provided nothing of value to me for their 20% charge. Cheaper options do exist now...
There's a lot of hand waving, but if you trust paypal, which you probably should not, the cost of moving money internationally has dropped to about 5% and the cost of currency conversions has dropped to 4%. I would assume they double dip and converting USD in USA to swiss whatevers in Switzerland would cost about 9%. Then of course there are withdrawal fees and so forth stacked on top.
Anyway, lets say you can turn and burn bitcoin in "somewhat less than an hour" so simply divide total international daily transaction volume by twenty five or so and that seems a reasonable starting point for a store of value. If the price gets too high making it cost more to use BTC than paypal, then the BTC transaction volume would seem to drop until prices drop and people start using BTC again.
Obviously for various UI and enduser reasons I would not expect all international trade to flow over either BTC or paypal or the legacy banking system, but "enough" should be there to support the BTC price at some level.