More theme parks should do what Disney does, which is the Dining Plans. Regardless of the higher cost, if people think they are getting value for their food, the park benefits from more patrons that prepay their food. Otherwise, guests will be cheap by design and try to bring food into the park.
I brought food many times to the parks. Of course, it is hidden in my backpack. Sometimes I don't if I am lazy or it doesn't matter on occasion. In my next trip to Disney World, I will take advantage of the Disney Dining Plan. I realized that in this trip, I prefer to take advantage of the character dining. There is no way to do this cheaply. I might as well just save the money and spend it as an entertainment expense.
Bad food is a problem, but I haven't gone to Six Flags in over 10 years. It is discouraging that the food quality is so bad and the prices are so frustratingly high. The bright side is I don't do this all the time. The food court at the local mall is just as bad and just as pricey.
As we are not able go to WDW or Universal, I happen to love Orlando, very often we have noticed that the food has gotten better between our trips. In 2010 it was nearly impossible to find non fried food at Disney, in 2013 there were a reasonable number of choices available, not a lot but a start. However as said before I will not go to Disney and not have a turkey leg or ham hock, you just do not mess with some things.
I am glad that you brought up Six Flags Great America. Their food is not that great. They have gotten better, but nowhere near the big parks. Is competition a factor? Maybe. SFGA is surrounded by Outback, Joe's Crabshack, and a McDonalds.
Just some insight from someone who lives not far from Chicago in Illinois: almost no one I know goes to Six Flags. It's quite a drive from the city and there is no convenient way to get there from Chicago other than car. No train or anything. Most people who live in Chicago itself don't drive (and instead ride trains and buses). Those who have cars don't seem to ever think of driving out to Six Flags. There's too much to do in Chicago itself and a lot of it is free (festivals, concerts downtown, just the lakefront itself in the summer with the beaches). Going out to an amusement park when you live in Chicago with so much to do is just a strange thought.
My family is out in one of the suburbs south of Chicago and we never go to Six Flags. That park has a kind of rough element sometimes and a lot of teens who would shove my boys around. It gets violent at that park at times. Every once in a while we get free tickets to Six Flags from my husband's work and even then we don't go. It's just not worth it because we have a better time driving into the city and doing something fun in Chicago.
That's just one family's take on it, but it might be why Chicago only has this one amusement park nearby. There's also Navy Pier in downtown Chicago with a few amusement-type rides that seem to satiate any craving a person would have for an amusement park.
This same theory happens everywhere you have a captive audience. Movie theaters, concert venues, stadiums, airports, highway rest stops, and airplanes. Anywhere it is either difficult or impossible to leave and re-enter, owners are going to leverage that against the consumer. I don't blame them for taking advantage, but it comes down to the consumer to refuse these actions, which are practically blackmail. The only way businesses will change their practice is to demonstrate to them that they will make more money if they simply offered a good value instead of trying to gouge consumers for every penny they have because they have no other choice. When a theme park realizes that good food at reasonable prices sells better and creates more profit than nasty overpriced food, then they will start initiating change.
It should be noted that I'm not saying the price of theme park food is THE problem, perse, more that it is a problem when the food being served is not good. At Disneyland I'll usually pay the $10 for a plate of [whatever] because it's good food and I know that the upcharge is what I'll get at a theme park.
On the other hand, I just snack all day at Six Flags Magic Mountain or Knott's Berry Farm because the food just isn't good enough to justify the cost (even if I accept the fact I'm being reamed for being in a theme park).
When I worked at Disneyland, there were three cast member only restaurants and those were augmented by a couple of food trucks. The only guest restaurant (when I was working there) that served cast members was Village Haus -- and even that wasn't all the time.
Annette -- Great to hear the perspective of someone who lives in the area. I brought up Great America because it's an island in terms of theme park exposure and reaps the benefits in terms of attendance. It's a shame you haven't had good experiences there; I hope to make it out there myself some time in the next couple years.
As for the Taco Bell comment...I'm so, so sorry.