You can also get a bus pass for like $1/day instead of paying for a car and gas. So that $200 in gas gift cards is really only saving you a few dollars, because normally you'd pay for a bus pass, am I right?
Are you one of those suckers who PAYS money just to live in a house or apartment? That's a waste of money. Instead, go to your local sporting goods store and buy a tent (if you're sneaky, just steal one, save even more money). Now you can just live on the street FOR FREE! Doesn't cost a single penny! Waow!
What about a $500 gift card to target? Well, using your theory, that only saves you a few bucks too, because you can go to the $1 store, thrift shops, and the goodwill to do your shopping.
But for most people who aren't going to eat the same meal every day and only spend $10/day on food, there are some definite savings in getting comped meals at casinos. I guess I probably spend about $15-25 a meal when it's not comped. Neither I nor any other AP I know count food comps as part of their earnings. The only thing I consider is the money when dealing with earnings. Exception would be if I can play to get gift cards to something I'd already be using (like gas gift cards, mainly). Food, rooms, etc. is a nice benefit, but that's all those things are -- benefits.