I think it is more useful to imagine bitcoin as an internet success, not a world revolution. If bitcoin were as successful as a facebook, or a twitter, widespread, ubiquitous, with apps on smart-phones and bitcoin addresses shown on billboards and so on. 21 billion dollars in bitcoin trade would make the 1000 dollar bitcoin about right I would say. I'm not sure how a 21 billion dollar bitcoin economy compares to something like facebook advertising and data-mining revenues annually. Perhas it would be necessary to talk in terms of estimated bitcoin GDP.
Facebook/Twitter is little more than a fun toy for most users. Bitcoin is potentially way more useful and serious than that. It takes the internet to the next level.
I'm not saying that Bitcoin will ever have as many users as Facebook, but
if it does, market capitalisation will be orders of magnitude higher than Facebook's.