Ken, at world titles in Laser class dinghies, the jury can watch out for repeated rig movements from a long way away. If they see something suspicious, they move closer and closely monitor that boat. There seem to be surprisingly few people who change their pumping behaviour when the jury boat comes close - perhaps they realise that if the rig movement suddenly changes in pattern, the jury will watch them even more closely later on. Getting a non-discardable DSQ or being chucked for the whole regatta is a major issue that sailor take care to avoid!
Sure, we take the rules to the limit - but we stay within them, just like tennis players try to hit to the limit of the court but stay within them. In my experience, at the point end of national titles in Laser Radials and other boat classes and in Windsurfer One Designs, illegal pumping just does not exist as a significant problem.
Maybe a lot of the problem will be cured by the fact that these days, we can just give every rescue boat a camera so that people will know that the PRO will have hard evidence to give to a protest. That wasn't so easy when pumping rules were relaxed.
ZedZed, I may be like you in that I was in Raceboards in the '80s when unrestricted pumping crept in (more because the wind limit was dropped than because of any rule change; pumping was always allowed but not critical in races in 20 knots on old rigs). What I can recall is that even at the Worlds, no one was pumping as hard as they do today. When we allowed unrestricted pumping in, I don't think we visualised the current situation of people pumping non-stop and not even tacking on shifts (according to a recent RSX worlds runner-up), and where people pump so long and hard that we have to limit the number of light-wind races so they don't collapse from heat exhaustion. That just was not on the radar, so decisions made then may not work for all classes today.
I got out of D2 before the pumping rule was relaxed, but a D2 Olympic medalist who went on to win an IMCO worlds says that while unrestricted pumping DID make windsurfing more athletic, it also DID mean that the gaps in the fleets became much larger and tactics much less important, therefore taking away a significant amount of the fun. And I never heard of anyone in the little bit of IMCO racing I did who really enjoyed a light wind pumpfest, whereas a light-wind race in classes with no pumping can be very enjoyable.
Of course, even if the majority of modern Rsceboard/RSX sailors like pumping, that's a slanted sample because many more people may already have left the sport because they hated all the pumping. If continuous pumping was so much fun, why does FW advertise the fact that it favours pumping less?
Surely it's rarely if ever just a matter of either staying off the plane, or pumping to plane. If the conditions are that marginal, you probably won't plane for long, and someone who pumps until they are exhausted will be faster. That's fine for many sports and many classes in windsurfing, but it's not what all of us want all the time.
Having some classes with pumping restrictions just gives us a bit of choice, that's all. And it CAN be done effectively, as proven in other classes.