If you are still making gains I would stick with what you are doing now for at least another 6 weeks and see what further gains you can reap, as for leg power I feel that contrast training is one of the best methods to achieve this, performing a weight exercise followed by a plyometric body weight movement, as you do not list the type of track work you will be doing it is hard to gauge the volume and intensity of the weight room work, 2 sessions a week in the weight room where one is a strength speed session and the other a speed strength session would I think be appropriate in most situations, for this I woudl do the following:
Session 1 – Strength Speed
6 x 3 @ 80% 1RM
2 exercises – 1 x Olympic, 1 x Squat
Session 2 – Speed Strength
3 x 6 @ 40%
3 exercsies – 2 x Olympic, 1 x Squat
you can use different exercises for each workout, you can also do a lower body plyometric after each set of the weight exercise, for the same number if sets and reps, cheers, ash