I went to my first SDCC in 2007. It was amazing in terms of how much was there, and the scope. There were more people there than at any of the Star Wars Celebrations I had ever been to, and those shows are big. I went back to SDCC 2 years later in 2009, and WHOA. It just turned into this huge Hollywood extravaganza. EVERY major movie studio with a comic or fantasy title on the way was there in a big way. The original spirit of the con has turned into something else, and has definitely been co-opted by Hollywood into one of the biggest promotional events of every year.
The attendance in '09 was out of control! One cab drive I spoke with said that the estimates on the number of people in town for SDCC was in the neighborhood of 200,000. Walking the floor bordered on scary at times because it was simply a crush of people. And good luck getting into some panels.
As for the facilities? The San Diego convention center is really big. But is it THAT big? It's been a point of contention for several years now that SDCC has outgrown San Diego itself. Especially with cities like Las Vegas hoping to lure Comic Con away. Vegas definitely has far more to offer Comic Con attendees in terms of accomodations. It's definitely an attractive option since both times that I went to the con I had to stay about 20 minutes outside of San Diego proper. And that's a major consideration for a lot of people who attend Comic Con. Las Vegas's convention center has monorail & bus service to and from most of the major hotels. And Las Vegas also has a much bigger convention center than San Diego.
These attempts by San Diego to expand the convention center really do seem like a stop-gap measure to hold onto Comic Con. And how can the city REALLY hope to increase the number of hotel rooms in the downtown San Diego area?