I'd love to know, for anyone willing to share, an approximate figure of what your 2019 income was. It doesn't have to be detailed, like how many cards and or how many sales, but in general, I'd like to know if this is a 20-40k/yr side gig or a 2-4k/yr side gig. I have some valuable cards and could start applying for new cards to season them, but I'm only really interested if this really is a 20k-ish side gig.
It likely isn't a 20k+ gig anymore, but solid low five-figures if you have the cards. If you're seasoning new ones, it won't be. Then likely low four-figures. If you just have a single card or two that's eligible, low three figures.
First, it depends on the details of the cards (their limits and ages and especially how many you have enrolled) for how many sales you get.
I know a few people making low five figures (10-15k range) per year. Based on information I have of MMM members, I'd say the average person has 1-2 cards enrolled, sees a sale or two every few months and makes $600-$1500 per year.
Regardless of what you make, the main benefit is the lack of time/effort required. It pays about $1000/hour because it takes about 5 minutes to add someone, 5 minutes to remove them two months later, and you get paid $150-200 for that effort. So whether you're doing it 60+ times a year and making 10k+ (and spending 10 hours a year doing it) or doing it 6 times a year (and spending 1 hour a year doing it, making about $1000 doing it), the effort to amount ratio is well worth it, for me personally.
If it's only worth it to you if you make 20k doing it for 20 hours (~2 hours/mo, say 10 AUs/mo), it likely won't be that. You'd want a dozen+ cards, old/high limits. More doable if you have a spouse with lots of cards.
I think it's most valuable for those new to MMM--still getting their financial stuff together, perhaps in debt, wanting a side-gig to accelerate things, but don't know where to start or don't have a lot of time. Even a few hundred or few thousand bucks can make a big difference to them, and the amount of effort or energy required is so low that it's huge to them.