The fish and inverts will have problems long before the plants will. But the problem with all the bubbles isn't because you have too much CO2 in the tank, but because the CO2 isn't combined with the water. It's still separated. Therefore, you can actually see it. That's the nature of an atomizer. Some people like it, some don't. To me, it's distracting and wasteful, but as you said, CO2 is cheap.