We do not know whether the number of "bitcoin users" is increasing.
Yes, we actually do.
blockchain.info stats aren't the only source saying so. [ ... ] Your argument runs down to: but all those stats could be faked/manipulated by entities high enough in the decision chain of exchanges or websites. While theoretically
possible, you have to ask yourself it is the most
likely explanation of the data. [ ... ] There's plenty of fraud and deception in the Bitcoin ecosystem, but what you seem to have in mind is a level of organized deception that you cannot simply "claim" to be the reason for the data. If you have solid proof for it, let us know. Otherwise, I could dismiss anthropogenic global warming by claiming that measuring stations world wide were manipulated by Jewish space lizards -- it's a possibility, y'know.
By "fake" and "unreliable" I do not mean
intentionally falsified (although that is a definite possibility, since almost everyone in the "bitcoin industry" would have a strong motivation to do that).
Take for example the plot of
total estimated daily USD transaction volume by blockchain.info. (That plot is obtained from the
total estimated daily BTC transaction volume times the market price. The "estimated" in the name refers to the exclusion of any transaction outputs that are assumed to be return change; I do not know how they do that.)
Note that the USD volume during Jan/10--31 was ~75 M$/day; in Mar/25--Apr/20 and Jul/10--Aug/05 it was ~50 M$/day. So the USD volume dropped 30% from January to now, and did not increase from April to now (although there were some peaks in between).
That does not fit with "increasing adoption". The only way to avoid that conclusion is to assume that most of that blockchain volume is not actual payments (bitcoins changing hands) but "fake volume" (bitcoin moving between addresses that belong to the same person); so that the presumed increase in actual paymets is masked by the "fake" volume. Indeed, this hypothesis is consistent with the claim by Bitpay that they processed 100 M$ payments for the entire year of 2013, with is only a couple of days' worth of the USD volume shown by blockchain.info.
But if most of the transactions in the blockchain are "fake", the other blockchain statistics are equally meaningless...
Online wallet stats,
Would you have a link for this data?
number of vendors accepting Bitcoin
As I wrote before, these "adoptions" are unlikely to attract many new users to bitcoin. They are attractive only to people who already have some amount of bitcoins and have decided to spend some of them. New users who try paying for something in bitcoin, out of curiosity or hoping to save money, may be disappointed rather than "converted".