When you run faster you automatically start to run better
When you run better you are motivated to find out more about how to run even better
That's the magic of running faster.
Once a year you should choose a run to do your fastest - no matter what the distance - 5km or a 10km or a half or full marathon or perhaps an Ultra.
Then train seriously for it, with other events if any, en route being strictly training runs and not a flat out event - else you are likely to get injured en route to your goal.