From a compete outsider just a simple question... what is the difference between a SUP board and the older style "Windsurfer" or similar boards?
And what is the main attraction for SUP?

My friends and I ,years ago ,tried sup on an old wally windsurfer.It was OK ,but as longboard surfers we decided that we would stick with longboard surfing.About a year ago we decided to give it a go again ,this time with an11'6" Naish Nalu.The difference was very obvious,we got hooked on it pretty much straight away.Now we paddle and surf when the swell is small,paddle when it's flat.Have to admit to going back to the longboard when it gets bigger,only because my skills aren't quite as good on the sup,but getting there.My advice,demo a real sup board of a suitable size for your weight and ability,you will be back for more.

en.wikipedia.org/wiki/Windsurfing

To ensure my following story is roughly correct, I checked on Wiki...

Windsurfing started to become vaguely popular in the very late 60's, and gained greater traction in the market through the 70's.

The article (above link) confirms that the early windsurfers were based on 1960's malibu surfboards. These boards had very soft rounded rails, and are not "high performance" orientated boards. Modern day "Longboards", SUP, and even windsurfers have much harder/sharper rails. These Modern day boards are also lighter and have more durable construction, better flex properties, and the fins and fin set-ups can be explained as being "100% to 1000% better".

Modern SUP surf boards are vastly different to the old windsurfers.

Get in touch with some SUP riders or a SUP Club in your area, and they can run you through the massive differences, as they give you a few tips on paddling, and paddle technique.