Actually, I think we can go much higher on speculation alone: $1,000+ easy. There are tremendously huge funds being stuffed into BTC from very wealthy and powerful people. As price climbs, it encourages a much larger financial status/risk tolerance and pushes entrance out of plausibility for the middle class investment - many of whom already looked at BTC as a fad/bubble/ponzi/..or just simply hard to accept in concept; now telling them they'll need to cough up over $600 for a single BTC, they're likely to respond with the same, if not greater, level of reservations and skepticism.

If this train keeps chugging along, and we find a level of stagnation combined with still little merchant acceptance - Look Out!! Fortunately, merchants seem to becoming more privy - even the large ones - at what they have to gain by accepting the precious.