There are definitely times when you need to make choices; you have a finite amount of time and energy and you can't put all of it into customer service. I too would suggest that spending all your time providing perfect customer service to a few customers is probably misplaced effort.

You can always make sure that all your interactions are as pleasant as possible. That will cost you very little time and will leave a lasting impression.

Today I had my first (and hopefully only) encounter with Dreamhost customer support. I was trialling a setup for a client who was looking to host 3 sites with them. By no means a big account, maybe not worth their time. Because of the way I was treated I will have nothing further to do with them as a company if I can possibly help it. I will never use them myself and I will never recommend that my clients do either. Had they taken the time to offer me courteous support I could have gone away happy and the entire process could have been completed faster. Sometimes you don't even need to be nice, you just need to show some manners.