- Edited
Here's my idea of how they should do it. There should be no limit to the number of levels you can level up but each higher level (in a day) gets you a lower chance of getting nemo bucks or egg coins.
The first level up would give you something like these chances:
20% chance of 2000 cookies
50% chance of 1 egg coin
30% chance of 200 nemo bucks
but then the next level the egg coins and nemo bucks would both decrease by 5% and the cookies would increase by 10% like this:
30% chance of 2000 cookies
45% chance of 1 egg coin
25% chance of 200 nemo bucks
the next level:
40% chance of 2000 cookies
40% chance of 1 egg coin
20% chance of 200 nemo bucks
and so on until there is 100% chance of getting cookies and no chance of getting something else. This means that somebody who plays at least five levels would almost be guaranteed to get 200 nemo bucks and 2 egg coins at the very least (and 1400 nemo bucks and 14 egg coins in a week). The chances would of course reset each day. I believe this is the best of all worlds for these reasons.
Players would have good incentive to play for a lot more than 30 minutes or whatever. There would still be a cap though for the amount of nemo bucks and egg coins. Lastly players who don't have time to play that much still have pretty good chances of getting egg coins or nemo bucks.