I think the real question is what you are looking for - whether it's a high-end splurge special-occasion type place, or very good food. You can spend $100-200 per person at Everest, Ambria, or Tru and you will get a wonderful, memorable meal. For half as much money, you can get an excellent dinner - seafood at Shaw's or Joe's, Italian at Maggiano's (not part of the LEYE chain, but they honor, and sell, the LEYE gift cards), tapas at Cafe Ba-Ba-Reeba, steaks at Wildfire, Chinese at Ben Pao's, etc. Which is the "best bang for the buck"? That depends on whether you're looking for a splurge kind of dinner, and are willing to pay the higher price it costs.
I've been to all the places I mention in the previous paragraph, and all are worth going to. The places I didn't mention are either lower-end places (not necessarily less "bang for the buck" but I wouldn't compare lighter fare with real dinners) or else they are places I haven't been to. Please forgive the omissions.
If I had to stretch a $500 gift card into three dinners for eight people, that would pretty much rule out all the splurge places. You might or might not be able to squeeze in eight dinners for $500 at places like Wildfire or Shaw's, depending on what you and your companions order (particularly in terms of alcoholic beverages). Will you be able to include the $125 in somewhat-restricted bonus certificates (that you will receive if you buy the $500 gift cards this month) in your calculations, so it would be $625 instead of $500?