Pull out every idea you have there and have a test. Your main goal was to motivate users and not you should be motivated by them. If you or your team will add some exciting stuffs then that will be the start of motivation process.

I take a quick look at the site. The registration process should be fine with just username and email. Although anyone can put fake names on first name and last name, it's really not a mandatory to have those required infos during the first phase.

Well then Goodluck.