One of the workers at trek when I was there had a frame nickel plated. He said he wanted something different, because everyone gets frames chrome plated. So somewhere out there, there is a '70s trek that was nickel plated.
I always thought it was a bit blah. I have machined hard nickel plate and then it looks okay, but it's still like a dull chrome. But it shouldn't rust if the plating was done right. Raw, it looks like one of those hot dipped galvanized exterior nails.

I don't remember anyone getting a Trek chrome plated around that time. That would be pretty neat.