First, I'm not sure why you need to increase speed in the first pull. Do you mean strength?? The first pull is not about how fast you pull/break the bar off the floor. It's more about control and setting up for the second pull (above the knees). The second pull is where the speed/acceleration comes in. If you break the bar off the floor with too much speed, you can lose your positions and bad things happen (i.e. you lose the lift).
Second, there is nothing wrong with hanging on to a pull and lowering it after reps. I do this all the time. I know there are some people who prefer to pull and then let the bar drop, but not me!! Maybe this holds me back?? I don't think so as I can pull more than I can snatch right now.