-Strength can be developed without putting on a bunch of leg mass
-Dynamic effort method can help, however, its relation to sprinting is minimal. This has been covered many times here on this site. Perhaps the only way it would have a direct transfer to faster sprinting is in a beginner. After that it is better to focus on general strength in the weight room. The speeds reached in a dynamic squat are nowhere near the speeds reached in sprinting.
-Mass is necassary for any sprinter, however there is an optimal range that will vary according to the individual.
-Muscle density can be trained on the track and the weight room, without dynamic squats.
If your goal is for speed, perhaps you should stick to a more basic approach and leave dynamic squats for the powerlifters. If you post some info about yourself I am sure others would be willing to help.