Slow paddling won't increase your speed, period. But train smart to race fast is possible. Training should be based on your goals, of course. If the race distance will be ten miles or less, and if you're racing to finish and have fun, then a simple training plan will work. Time will dictate what is possible.
So, you can't do seven, then do five, but never miss the pre-race day or the race kicker. Heart rate training works for me. My rest day paddles ranges from 105 to 120 bpm. Interval days range from 100 bpm to 150 bpm. Distance days are in the 120/30s for what ever distance. My race pace is 146-154 bpm with max as high as 180. Why do the kicker? It's because you can go flat out from the start of the race without going into oxygen debt. Try it, you like it.
While I think slow paddling won't make you fast, it's needed as part of a training plan to keep training fresh and not boring. Some days it's just nice to smell the roses. Have fun is the whole game. Smile.