You'd get the same smile if you had no dining plan. The smile you are seeing is because of "no
ddp", not because of "yes TiW"
I think what you're saying certainly applies to a comparison of TiW vs. DDP. But, for TiW vs. paying out of pocket, I really don't think so. I don't know what the average tip is for out of pocket payers at signature restaurants, but I bet it's higher than 18%. I know that In my case, they get significantly less tip because of the automatic 18.