If the price weren't fluctuating at all, I would have all of my money as possible in bitcoins. In fact I tried during the long 5$ period last year. I don't use myself as an "investor", but as an user that has its own bank. There were several potential purchases last year that I didn't make because I had to go to the bank, do transfers, etc.

Potential clients includes investors, but also users that just want to save in bitcoins. It doesn't matter that merchants convert the money into USD, the other advantages still applies.

Also, PayPal is very expensive for very small purchases.