I don't buy much at our (stateside) commissary. The meat is CAFO and the produce is old; it goes bad within a day or two. And I don't care what they say, it's NOT cheaper than off-base, unless maybe they're basing that on the price for cat litter and dog food.
Good luck with writing the commissary and dining facility folks. I can't see that much will be changed, it all comes down to $$ and the crap "food" is cheapest. I'd recommend that you send copies of those letters to your government representatives. Not that our gov't reps do much, but sometimes they'll jump through hoops for military folks.
Do you have to eat in the mess hall? Can you get something from a military doc that will let you out of that? I'm sure there are people with allergies or other food sensitivities that don't have to eat in the dining facility.