However the OP asked if YOUR standards lowered, not if the standards/quality of the food has lowered due to free dining.
To which my answer is yes.
Don't get me wrong, I love the free dining plan. Take every advantage to get it.
But if I have a so so meal at one of the restaurants, I would be more apt to take the "oh well, it's free" approach.
If I were paying a large amount for that same so so meal, I would be more likely to not return to the restaurant or maybe let a manager know it wasn't great quality for the price.