"I am inclined to agree with the conspiracy theory that if these secondary stats were any good, we would be hearing about them."
I don't think it's that simple. Google publishes very few figures that have to do with its core profitability. For example, number of searches a day is not reported. I doubt it's because that figure isn't any good.
But in this case, Google is publishing numbers. Numbers that by their own admission aren't even trying to measure the right thing, and which seem to over-count that wrong thing anyways. Given that they're publishing any numbers at all, why are they publishing those numbers in place of more relevant ones?
Well, that's assuming people actually believe what Google. And even they believe what Google says, they don't have any compelling reason to switch from Facebook until their friends actually do switch.
What I mean is that even assuming that people believe google's statement of "it's not a ghost town anymore", they are probably not going to move until it actually stops being a ghost town.
That is because they have little to gain by announcing the number of searches because they're already way on top.
On the other hand, if G+ numbers were good, they would definitely announce it to increase the hype and get more people to check it out, out of curiosity.
I don't think it's that simple. Google publishes very few figures that have to do with its core profitability. For example, number of searches a day is not reported. I doubt it's because that figure isn't any good.