Part of the reason I branched off (or returned to, since I was doing these activities semi-regularly about 15 years ago) into swimming and biking is that I was bored with just running. I also did not feel like I was getting into better shape just running. I think combining the three things has helped me get in better shape overall.
After the first race, I fell in love with the feeling I got racing, before, during, and after.
The racing aspect fills something in me that is missing.
I think the feeling from racing is the biggest thing. Whenever I get down about training, I think about racing, and it helps to motivate me.
I think the best I can hope for, the best, is probably top 5 in my age group. So racing isn't about being the best against other people. It is about challenging myself and trying to do better each time I go out. If not the whole race, then the swim, or the bike, or the run, or transition.