Some additional moderators wouldn't make a dent, especially if they're community moderators. ROBLOX would need a whole new team of full-time moderators working around the clock. Moderating user discussion is not easy.
Not everyone is looking to be a great person. There are these people that exist called "trolls". These people, as well as the type who have authority issues and hate moderation, would never see improvement from being surrounded by others setting a better example.
No. Anyone can nominate, including users who've compromised devforum accounts, and anyone can be nominated. This would nearly immediately result in someone, owner of their account or not, dropping in hundreds of users for nomination. We already had this problem on our unofficial devforum Skype because everyone had permission to add users.