What/why do you sail the cat you have. Why does that particular model appeal to you?
Started on a Prindle 16, later added a Prindle 18. Still had the Prindle 16 when I sold the Prindle 18. Then I decided to upgrade and got the first F16 in existance. I had to sell my P16 to pay for the F16, for some reason that never sat right with me although in hintsight it was the best thing to do. Currently Prindle 16's are dying overhere (no spare parts) and the resale prices are ludicrously low. And I'm loving my new boat to bits although the owners of the new models do attract my jalousy !
Attraction of the boats. The P16 was simple and quick to rig and could still be sailed well singlehandedly as well as doublehandedly, including righting it. If I'm ever in the market for such a boat again then I think I will go for the Nacra 500.
The F16 is all of the above but significantly more performant and it has the spinnaker of course. I'm addicted to spinnaker sailing. But the next most important point for me is that I can directly race the F18's and F20's in my club races. With the Prindle 16 you are always in the back of the fleet and even if you have an excellent start you'll be breathing bad air within 5 minutes of the start. It is alot nicer to play alongside all the others.
Wouter