This is alot of fuss over something that is, in reality, all a matter of perception. If you are looking for an excuse to not attend, please by all means find an alternative that you will be less likely to upset yourself about.
If you arrive at 7pm, get your photo on the west side of the park during the first parade (8pm), circle the park clockwise for attractions, trick-or treat after the second parade (10pm, when most people leave) and stay until the end of the event, I think you will find yourself pleasantly surprised with how much you can get done. My opinions are based on actual first-hand experience over the last 5 years. The estimates presented in the unofficial guide are not provided by Disney, they are the same or similar to the estimates used by Amusement Business Weekly magazine, and while they are a reasonable estimate, they are abstract numbers if you have not seen conditions in the park compared with actual attendance numbers (those estimates are the number that have passed through the turnstiles, btw, not the number actually in the park at a given time). The difference between 20,000 and 25,000 (niether number has been given, btw... the company advertises "a limited number of tickets sold,") is inconsequencial. If this is your biggest worry, you should have a wonderful visit because you must have everything else taken care of.
Have fun.
*Edit* I have the halloween party on my brain because that is what I am currently dealing with. With regards to crowds during the Christmas event, my statements stand. View the second parade, get your photo/cookies and cocoa during the first parade, avoid the normal flow of traffic, and have fun. If you are going primarily for the special entertainment and your visit will last beyond Dec 18, I agree with previous posters that you would be fine just to skip
MVMCP, as the entertainment becomes available during normal operating hours after the last party event is over.
No one who has the actual ticket sales information will be reachable by phone, and no one who you will be able to speak with over the phone will be able to give you actual ticket sales/attendance information. You would serve yourself better to spend time and energy on other things.
Again, have fun!