Allowing users to enable features by post count would be nice. First, there are a lot of (human) paid link spammers who sign up, post some gibberish marginally related to the topic, and add a bunch of spam links. Second, it's nice to give people a spiff for contributing.
However, I'd like to also request an administrator-settable time enabler with this. For instance, you must have 10 posts AND have been registered for a week before you can post links, or you must have 30 posts AND have been registered for 30 days before you get an avatar. The problem with doing it solely by post count is that people flood the board with a whole bunch of annoying gibberish in order to boost their post count.
This could probably be done by allowing users to be automatically promoted to different user groups depending on post count and time…then the permission sets would take care of the features.
Anyway, it's an idea to consider. Thank you for all the work you've done to make SPF clean and usable!