Even if the service is not part of the experience, bad service can easily ruin it. If you need to wait several minutes before someone gives you a menu, then you need to wait another 5 minutes before you can order and then again you wait another 5-10 minutes before you can pay, that pretty much ruins the experience. This is quite common at casual restaurants here in Germany and annoys me every time, especially in the first weeks after returning from a trip to the US...