That is hard to answer because I don't know exactly what you mean by lifting weights at high speeds. To increase explosiveness especially you need to have do very specific exercises and train with very specific form. You really need to know what you are doing or injuries are sure to happen. Your overall thinking is pretty much true. Doing the positive part of an exercise in an explosive and direct manner will improve power and will develop a fair amount of muscle gains. But I suggest you talk to a trainer and tell them your goals so it is set up properly.