If the food is disappointing, I don't go back at all. If the food is great, I can probably survive all sorts of service problems as long as the food arrives in a condition that renders it still great to eat and the price is in line with the total package received or at least it's difficult to find better value elsewhere. They can actively increase your business, both through effective selling and by building a regular clientele. Probably true, but on the individual level, I doubt a great server could sell me anything if he couldn't serve me great food. I suspect a great server could be trained in shorter time than a great cook.
Great cooks are far rarer than great servers.
I'm looking forward to the can of worms you've opened. We'll see how hot a thread it is. My great disappointment with the group has been that threads relating to ketchup and free refills of soft drinks tend to run longer and hotter than serious discussions of fine food. Allow me to play Devil's advocate too. I often have the feeling the average diner has some quirky need in terms of food and service but really would not recognize good food or service if it hit him in the face.