Yes adding a spinnaker is definitely worth the money. With the 580 you can add it later if you want to save some money up front. If you want to go the 580 route, get it with a boom..much better if you then add the spin later.

PC sells a complete spin kit.. You can also get a self tacker on the boat but the jib is cut a bit differently, so better to get this when you order the boat. Hull shape is very much like the N6.0, just a bit shorter. Rig is the latest design square top mylar main similar to the f18 but bigger.

But I think the biggest question is what are you going to do with the boat? If just cruising with the occasional open regatta then the 580 would be a great boat, but if you are really going to do the regatta circuit then the N20 is the boat..Also, there is a great difference in price, as you know. But for pure fun sailing factor, a 580 with self tacker and spin would equal a N20 for less money. If you buy the PC spin kit PC will not void the warranty, but if you put your own spin system on it, it just might.