To answer the original question: the reason to invest in Bitcoin now instead of once it's proven itself, is because by the time it's proven itself that will have been priced in. You can't beat the market by doing what everyone else is doing---you have to invest in companies and technologies with uncertain futures.

I bought bitcoins at $0.85 because I thought they were very, very undervalued, which only meant I thought they had a much better than 1% chance of eventually being valued at $85 or more. In fact I think they have a better than 1% chance of eventually being worth $500 or more, which is more than enough upside to overcome even my level of risk aversion (which is pretty high).

Putting money into Bitcoin is not a safe move, it's an aggressive one. If you have a place for that in your portfolio, great! Buy some bitcoins and hold them. If not, great! Put your money into something else, and only buy bitcoins as you need them for purchases.

Edited to add: Ignore the "Bitcoins are not an investment" responses. Bitcoins aren't designed to be an investment vehicle. Neither is orange juice. And yet the CME is lousy with investors trading orange juice futures. Anything you can buy now and sell later is potentially an investment vehicle.