To keep the game accessible for people who want to bet amounts less than 100 USD, the bitcoin denominated value of bets would have to be lowered with a rising BTC price, which will reduce BTC profits.
"It's currently making about 15 BTC a month"
What you are saying is that bitcoingem made 15 BTC a month with an average of 50 USD per bitcoin in march. In april the average price may very well be 200 USD per bitcoin and most people expect it to rise even higher in the long-term.
So there are two possibilities:
A. Keep the BTC denominated bets the same and potentially lose a lot of players who wouldn't want to risk 200-500 USD in a single bet; or
B. Lower the BTC denominated bets and reduce BTC profits.
What are your thoughts on this?
This is one of the things that needs to be A/B tested, anything else is a hypothesis or educated guess that we can all make and any of us could be wrong. However, I would be inclided to say that smaller bets would probably do better as it will attract more traffic to the web site so B could potentially be the winner. However, as I said, hard numbers usually prove things better.
Obviously the biggest risk for the investors is that HOLDING their BTC's would appreciate in value to 10x much quicker than a return on the site, thats a real possibility every possible investor in this should be aware of, but is also out of our control. I hope this answered your question.
-D