There isn't really any benefit currently other than helping the forum out greatly but if you report enough with a decent accuracy you may eventually get asked to be staff if an admin feels like you're needed (but don't hold your breath as shorena has around 10k reported I believe and still isn't a mod (though probably should be)). I was thinking it would be nice to offer some sort of reward for those that report a lot but it would likely be abused and I can't think of what perks could be offered other than monetary but then that would almost certainly lead to abuse unfortunately.
Yup. Tough to think of anything other than monetary rewards.
What could be done is one mod's pay subdivided among good reports (beyond a threshold).
As above people would likely abuse it if there was a financial reward. You could just create a bot to spam shit like NLC does and one to automatically report it.