The sensor bar is only for the pointer and doesn't affect the motion sensing capabilities. The Sensor Bar sensitivity determines the distance the player can be from the TV. If you move out of the range of the Sensor Bar the cursor can become erratic. The higher the sensitivity is set, the farther away you can be, but makes the Sensor Bar more susceptible to infrared interference.

As far as I know, there is no way to increase the sensitivity of the accelerometers (the motion sensing part of the wii remote)

Take note of the time it takes you to defeat your opponent, I'm willing to bet the time taken in the round is factored into the score as well as how "perfect" the fight was. Combos are definitely the way to go.. practice in the punching bag training.

For the super fast Tennis serve, it doesn't have to be at the top of the throw.. what's important is that you want to put the remote through as much of an angle as possible when serving. start with the remote angled back as far as possible (preferably horizontal with the remote pointing away from the tv), then with a brisk movement (not too fast) bring the remote through a full arc and stop when you get to the horizontal position with the remote pointing towards the tv. I usually do this with a flick of the wrist, using a comfortable, but quick pace.

Be careful using this serve on newer players, as they get frustrated very quickly