As for the racing, I do it for myself as well. No weakness in that, anyone in a race is busting their ass. I do enjoy finding out that I've done well for my age group (I'm 41), but I'm really running for myself.
I find that knowing that I have a race in the next month or so is great extra motivation for me to get off my rear on the days when I might otherwise pass on a run.
As a bonus, the people at a 5k run are super nice and helpful. I've been involved in other competitive sports and I've never seen such a supportive group of competitors. Maybe it's also due to current timing technology, because each racer (unless it's a very low budget event) is timed individually from the moment his/her bib crosses the start to the moment his/her bib crosses the finish line.
Oh yeah, have fun.
Oops. Sorry for the slow reply.
My personal theory, is that since a person is timed remotely as they cross the start finish line, there is no competitive pushing and shoving and jockeying necessary at the start of the race.
Before each person was timed individually, I imagine there was a boatload of jockeying for position at the starting line and made things more intense.
I've only been running races for a couple of years. It's just my guess.