I disagree on this. Those of us who have gone long enough and have gone frequent enough know the numbers and knowing what attractions are closed and what attractions are open can do intelligent deduction of what 10K vs 30K means.
On top of that, again those of us who have been there an an average Disney summer day, who know what the average summer day is can make an educated guess what the numbers are, relative to each other. I've been to the Magic Kingdom on Christmas Day so I know what max max max capacity is. I've also been on an average day, and knowing what the average attendance is, I can safely say 30K would be too much for me.
No that number may not mean much to the "average" guest. It may not mean much to a first-time or sporadic guest. But for the ones going right now, the die-hards, the lifers....they would be able to reasonably deduce what 15K people in the park looks like.
And yes, people in the park are spread out....but they won't be if they up the capacity number to 35-40K (And theoretically, they could, because no one knows the numbers so they could make capacity whatever number they want) ....and to do that without guests knowing about it.....I just don't think it's right, personally.