I believe people thinking a banking collapse in Greece is fuelling a rally is purely psychological. The price is being bid up simply on the idea that it should be bid up.
I think it's the same deal as Cyprus. I'm sure at least 3 or 4 Cypriots might have bought some BTC to help the price on its way up. All the other buying was from people who were already into it who took it as inspiration.
It's pure speculation as always. However the more it happens, one day the speculation will fall away and actual concern might fuel some buying. That's when it might get explosive.