I think the thing boils down to how much you need to get from the lettuce. If you demand the best of the best performance for your salad, you want to blot it dry with paper towels, so that the texture is best preserved and the appearance is undisturbed. For my purpose, in my kitchen, a salad spinner saves money (the paper towels), time (my time), and allows me to do something more interesting than blotting it dry, and the time saved can be used to better decorate the dishes I love better than the salad.
In essence, there is nothing wrong with any method of cooking if you enjoy the result, and it doesn't involve health problems. Spinning it dry is fine for me, and if you accept the result, there is little to hesitate using one.
Thomas Keller also told us that after vegetables release the flavors in the soup we should discard them, and replace them with fresh cooked vegetables with better colors and better flavor for better presentation. In my kitchen, I am not serving a Michelin 3-star soup to my family, and thus it is fine having those vegetables in the soup for some more fibres in our diet.
It is a matter of fine dining, it is not a matter of home kitchen. Insist if you have to, but relax if you actually can.