The problem I find with masks is that although wearing them does not affect oxygen or carbon dioxide levels, it is the layer between your mouth and fresh air which prevents easy deep breathing. I also find that I get headaches if I wear them for 90 minutes plus.
I know I might not be helping! But there are pros and cons.
But, as Hat said, how do you think you will cope with the noise and crowds of a theme park? Although we have come a long way, I think I speak on behalf of Hat and myself in saying that even we would experiences a few difficulties