The way I see it, it's like investing in the currency of an extremely promising, extremely poorly-defended nation. You could do really well out of it, until they get invaded.

It all comes down to how effectively you think the distributed consensus on transaction history is protected. A consensus which is not based in human relationships is very easy to pervert, given enough wealth.

The doomsday scenario, from my perspective, is China expropriating the mining farms in its jurisdiction, and constructing double spends until nobody trusts BTC as a means of transferring value. If that happens, there will be a huge rush to the exits. And it would be cheap, quick, and easy for China to do so.

There's a lot of money to be made in the meantime, though.