I agree with SoreCalf, he's done well. I also love getting medals, for the same reason, I'm crap at running and that I ever started was an achievment.
But I can also see where you're coming from on effort, though on a slight tangent...You don't sound like you've actually been in a race? I don't recall seeing many people in races, especially at the back who didn't look like they were trying? Except for those who, like I sometimes do, use a race as a training run, and yes do take it easy.
Regarding effort, you really do have to take natural ability into it, there's many who could train as you desribe, 10-20 miles a week, and make a good half marathon time look like a cake walk without trying.