You can check out a lot of stats in here: https://bitcointalk.org/index.php?topic=4428616.0  This is a post created by @DdmrDdmr in wich how many people have ranked is detailed.
Also check this, from the same author: https://bitcointalk.org/index.php?topic=3395255.0
In there, you will be able to see your own and other's merit networks.

Regarding the spam problem, no, there isn't, for the moment, any stats, but you just have to check out Meta or Reputation to make yourself an idea of how big the problem is. In fact, there is in crescendo, but, at least, most of the spammers become now "Forever Juniors", I mean, members with a lot of activity and zero merits.
The merit system is actually working, but just in the sense of the ranking-up problem.