All runners want to open up the stride and close hard the last 400 meters of race. Not only does it feel great to pass droves of competitors, but finishing strong helps motivate you for the next race. However, actual speed has little to do with how fast a runner can finish the last 400 or 800 meters of race.
As discussed above, most runners already have the absolute speed necessary to fly through the finishing shoot. A 20-minute 5K runner is probably already doing multiple 400 meter repeats at about 5:30 pace (60 seconds faster than race pace). However, finishing the last 400 meters of a 5K at 5:30 pace is probably next to impossible for that same runner. Again, the ability to kick and finish fast is not limited by absolute speed. Rather, the limiting factors are the ability to run fast when tired or to hit the last 800 meters in a less oxygen deprived state.
Therefore, if you’re a runner who is trying to improve your finishing speed or you tend to fade during the last mile, your training time would be better spent improving your aerobic capacity, not necessarily your absolute speed. Tempo runs and cruise intervals are going to address your late race “speed” weaknesses better than a steady diet of 400 meter repeats.