Sorry for my slow response. I'm happy to share some data with you.

At the end of November, there are 24,208 "real "Pinside accounts. That's the number of activated, non-blocked/banned/frozen/dupe accounts.

Of those 24,208:
...13,330 Pinsiders logged on in the past 365 days
...5,977 Pinsiders logged on in the past 30 days (of those, 3,440 have made at least one post on the forum.)
...4,456 Pinsiders logged on in the past week (of those, 1,984 have made at least one post on the forum.)

This year we have had between 7 and 35 new signups per day (depending on the day).

"Current Pinsiders online" count data was never stored anywhere, sorry.

I've included some analytics data graphs for the time period Nov 7, 2009 and Nov 30, 2014.
some_analytics.png
Note: the area marked "oops" was an analytics blackout due to an error on my end. We have no visitor stats for that time period.

As for new signups, this is the table:
2001: 1 Pinsider signed up
2002: 8 Pinsiders signed up
2003: 572 Pinsiders signed up
2004: 677 Pinsiders signed up
2005: 379 Pinsiders signed up
2006: 228 Pinsiders signed up
2007: 214 Pinsiders signed up
2008: 380 Pinsiders signed up
2009: 883 Pinsiders signed up
2010: 650 Pinsiders signed up
2011: 2164 Pinsiders signed up
2012: 5411 Pinsiders signed up
2013: 6449 Pinsiders signed up
2014: 6473 Pinsiders signed up (and counting!)

One can only guess why. Nothing was done that I know of.

Keep in mind, back then there was no forum yet. The only reason to sign up was if you wanted to add/edit the archive, do ratings, write stories. I can imagine there's a much bigger reason to sign up for the forum then there was for only rating games. (?)