Spitballing.

So to go off what you're working with here, something like what you're proposing would have a somewhat significant risk for abuse. Another site I used to go to had a similar system for reporting abuse. Basically it was a three strike rule doubled over. It actually worked really well, especially since the strikes were anonymous. The way it worked was as so . . .

User 1 posts or comments something objectionable. If three users striked it as such, user 1 gets a strike. Three strikes in a 24 hour period and they couldn't post anything for 48 hours. However, let's say user 2 strikes user 1 even though user 1 didn't post anything objectionable. If three other users unstrike user 1, user 2 gets a strike. Once again, if it happens three times in a 24 hour period, user 2 gets a time out.

Even though the system was anonymous, it worked quite well and was fairly balance. I never saw it abused. At the same time, people were very careful how they spent their strikes, for fear of getting timed out themselves. As a result, it was pretty much never used during heated debates, only really when people posted NSFW content, personal info, etc. I could see something like this working well for spam.