Fanbase is still growing. The atmosphere has significantly improved. Winning will help that. We'll see how much next year. It usually takes a year or so for that to show up in attendance figures. If they keep winning, they have an opportunity to have a very strong fanbase. It won't be on the Yankee or Cardinals level, but it can be very good. Too early to say it's there yet, though.
Do the Cards have a large fan base? The only time I see people in cards gear is when I visit my cousin in KC- they're popular in a huge swath if the Midwest, but it's not exactly a heavily populated area