IMO one way to get a handle on a reasonable value for 1 bitcoin is via this formula:

probability Bitcoin ultimately succeeds * value of 1 bitcoin if it succeeds

Bitcoin has the potential to become the dominant currency for large-scale electronic transactions worldwide. If this happens, bitcoins could be worth millions of dollars each.

So what is the probability of such a grandiose outcome? One in a million? Maybe so.

I see the recent increase in value as a rise in the consensus probability that Bitcoin will succeed.