Bottom line, what you're looking for is no longer served in San Angel.
When La Hacienda was built, it gave the San Angel group the opportunity to focus their menus on specific regions and tastes. When you eat in San Angel now, you will get a meal similar to what you would get if you went to the actual San Angel Inn in Mexico City. It's food that a real Mexican family that lives in the center of the country might prepare in their own kitchen. La Hacienda focuses a little on street food, but mostly on a menu that you might find in more coastal locales. All of the street food, fast food and Tex-Mex has been relegated to the Cantina.
San Angel's current menu is a vast improvement over the glorified cafeteria food that you remember, and it's your loss if you refuse to eat there because you find the unfamiliar to be disgusting. It has, in a matter of months, become one of the better restaurants in the World Showcase. As others have suggested, if a burrito is all you want, La Cantina would be more than happy to provide. You can even carry it into the pavilion and eat it while walking around the shops, if you're really pining for the ambiance.
