Limiting the number of "free" posts is an idea, but it may turn some people off to the site. There seem to be people new to analog (or just returning to it) who won't justify subscribing, just yet.
I'd probably open the Gallery up to everyone, for a week (or a month), let them post, or comment, during the "intro" period. My guess is it would get a lot more subscribers. At the end of the "intro" period, it goes back to subscriber only. Rather than turn people off, it could turn them on...