Interesting. I think I see what you're getting at.
Adding some settings for this stuff would be a good way to strike a balance between people who have few viewers, and lots of them. Can have some sensible defaults that work for both cases with the ability to tweak it in real time from the settings menu. Could also automate it based on the number of viewers, but not sure we understand the balance well enough to do that yet.
I've personally had the most fun watching when you have some amount of coins that you can use to bet and spawn things, but not an infinite amount. It's very easy to make it so you can change the coin generation rate if nothing else, so I'll probably look at that for the next update.
I agree that it might be a good idea to make the player able to turn off spawning certain enemy types, or limit the amount of spidertron 6000s you can spawn in a single round. It's fun the first time, but gets a little tedious. :)