as a coach and race director, I think both classes have a good part. Personally, unless there is a government support as for RSX, is not good to have a class that is one design as the Kona, as it limits people to buy just to one company, better if you have at least a chance to choose.
If you go Raceboard class, then Kona, RSX, Starbaord Hybrids and many others can race and that makes things easier for many people and also interesting.
I think Kona is a nice concept but thats it...its like saying lets compite in Serenity class. Can be good, but its not complete for what you want...say, an international calendar of events.
About fun factor...i vote for formula windsurfing, its the best thing in fun factor. Have not checked the costs between FW an Raceboard class as I am not updated of detailed pricing. Now FW is frozen in boards each two years..thats a good thing. Dont know exactly what raceboard class says about board designs.
Then, you can also have the chance of Formula Experience, is a very good class we would like to have here too. There are two boards racing there Bic and Starboard and lots of sails companies. If you can work in a good 18+ fleet for this class, then all your requirements are completed.
Personal view...from your choices...I will say FW, but again, dont have costs in my hands.