Dropping results for April... there is a drop in income compared to march but traffic and registers are increasing. I am a bit suspicious that cb might be shaving a fair amount of income. The ratio of people who spend money is pretty ridiculous. I am still having only 2 regular spenders and the rest are just occasional or one time. Maybe I am wrong but it just seems bit weird.
Well, that's not a significant difference to your March stats, the revenue is down by less than $40. Also, April is one day shorter

, your daily average for March is ~$25, so for 31 days the revenue is down by less than $15. If you thought that it will always grow until you stop promoting, that's not always true. Luck is a very big factor and you get only 100 new regs per month, that's not enough to be able to see a substantial grow and balance out luck plus those spenders who stop spending for any reason.
How many registrations do you have in the revshare program? I see you started in last June and i also see that you make 20-100 new regs each month (increasing tendency), so you are at around 500 free regs now, maybe a hundred more? Until you have thousands upon thousands of regs, there can be big ups and downs in the revenue, because it depends on a low amount of spenders. There can be lot bigger differences than just $15 per month.
In my experience out of every 35 free regs there's a spender, who's not even a regular one, just one who spent at least once. I have mixed traffic though, half of it is tier 1 and the other half is tier 2 and tier 3. If you have mainly tier 1 traffic, the conversions rates can be much better, it can go down to around 1:15, but i think you can consider yourself lucky, that you are able to hit these numbers with such a low amount of registrations.
Just keep up the work and if your registrations keep increasing, the revenue will follow.