Yes they are substantial changes. My post above was written at the same time yours went up so I didn't see it.Well, done some research. The Lightning site is a great place. It does look like this boat could be a good choice - thanks to those who lead me to it.
Now I'm looking at available boats. Given that I'm not planning national racing, are there any years/sail number it should avoid ? The Lightning site warns not to buy before 1990, and notes that the rigging was changed in 1986, and that newer boats have better recovery.
Are these significant things that I should be concerned about ?
I've found a nice 1984 Nickels that's near me and in my budget...
There are a lot of issues with a pre 86' boat, I touched on some of them, but they all boil down to a boat that won't self right (realistically) and is prone to turtling (almost unrecoverable without outside help). It also means you can't snag cheap sails from racers or use published tuning guides.
The boats are very different though they look the same.