TiW costs you $100. Then it saves you 20%. So basically if you spend $500 in food, the card pays for itself (that's food eligible for TIW discount). Someone did the math down to the penny, and I think the break even point is actually like $492 or something. 3 trips of 7 days each? Most likely you will make it up and then save some....but only you know for sure based on your sit down eating habits. Also TiW also includes alcohol at sit down places and lounges like TOWL.
TiW also adds 18% automatic gratuity. I don't include this in the math because I would have tipped without the card. If anything....as a typical 20% tipper....it saves me another 2%.