I dont know how serious you would think we are, but..

What Mary said, and the book _is_ good if you need exercises for boat handling.

In addition, we go out to work on our boatspeed with a GPS. It's far from perfect, but it's the best option we have. At least you can see the difference in pointing and speed with the different trims and techniques.
To hone our cutroath racing instincts, we have been allowed to race on handicap against the monohullers in their weekly races. Especially starts and the first 2-300 meters are nice training for our strategy and starting technique (even if they do timed runs while we park on the line). We have learnt how to point high and go slow from them at least, which comes in handy from time to time.

Now, we mostly set up a course and do laps while working on pointing, speed (up and downwind), laylines and technique. We keep a running critique going onboard, where we point out mistakes done and suggestions on how to improve in a positive way.
We have had some feedback from a few olympic T sailors, and the best feedback was the most negative one. It gave us a lot to work with.. Doing a coaching session with an open mind is a very fast way to improve. Sailing besides other types of boats can also teach you a lot on boatspeed, especially in light winds.
In the end, nothing beats time spent on the boat, working on how to be faster. Not just reaching around or running with the spi, but working on being faster on every aspect and manouver while going around the course.