So, years ago, TiW was a no brainier. That 20% off was actually just a little bit more for me:
Bill with Tax = $100. My standard is 20% tip, so i would leave $120
Tiw = $100 - 20% = $80 + 18% gratuity = $94.40
Anyway, that is when it was $75, so once we hit $400 at any sit-down restaurants, we were ahead. That was easy to do over a 13+ month period, and if we went with anyone else, perhaps easy to do in just one meal. Now at $150, you need to spend at least $750, and we have been trying to avoid spending that way. Plus our Platinum Pass has been getting us 20% at some restaurants as well.
But, if you are all in, TiW can still be worthwhile. And if you go with a large group, or plan to go more often, it can also work out well. Lastly, important to remember it works throughout Disney, not just in the parks. So, if you are in the area for some other reason, or planning a non-park day, it works at Disney Springs as well.