I can see mid-tier losing custom to the low-end (fast food or brown bag at lunch, grocery prepared foods at dinner). My impression of economic downturns is that the rich stay rich and maintain their lifestyles. Top tier may lose the once a year splurge diners, but the core remains.

I agree that Chilis/Applebees/TGIF qualify as mid-tier. I used to work for a company that developed POS (point of sale) software for the QSR (quick service restaurant) business. Our QSR customers seemed to weather recessions fairly well. We had some mid-tier casual dining customers who did not.