I run races as tempos all the time, I haven't paid for an entry at a local road race in years.
The RD usually asks me to run, and I do so for the sake of a hard effort.
I have my goal races every year, and those are the races I go all-out.
Of course I don't walk around saying it was just a workout, but it was.
I am not sure why some of you think you have to shit your pants and blow your load every time to pin a number on your chest.
Most of the time I will be training for a marathon, and jump into a few 10ks along the way to break the monotony of the track workouts. I can also usually help pace someone, improve the quality of the race time, etc.
I try to be respectful and not screw anyone else's race. I wouldn't be that guy who is neck and neck with someone until the end and then claim he only won b/c it was a workout. That is rude.