It depends on your rewards. This are my experiences:
When I started offering rewards it was rather stressful because first I offered a sketch commission for the highest tipper. However, I felt overwhelmed by the extra work (and uncertain payment since in some month the highest tipper could end up only tipping 50 Cents ), so I ended up dropping the reward.
Later I started it again with rotating rewards (pack of sketches, link to a video, PSD...), every month I offered something different. It was again quite some effort to come up with something new and some month hardly anyone wanted it. So I dropped the scheme again.
This time I kept it simple: one illustration which is recycled from Patreon. The artwork is already done and sending it via email isn’t too hard and time consuming either (especially since I ask my audience to contact me first.)
Rewarding supporters definitely is worth the try. So don’t worry about offering anything, even if hardly anyone claims there reward.
But you should keep it simple and try to avoid as much extra work as possible.
About the money. It varies month to month. In my worst months I made about $1.50 in tips. In some of my best up to $30. There are folks who make even more (or less). It’s unpredictable and you shouldn’t bank on it. But it’s always nice pocket money and definitely worth asking for it