First, polish it up by hand using a compound that specifically says it's for nickel. That will probably remove the rust and will make it look much nicer.
"Nickel" is actually nickel over copper over the base metal and is quite rust resistant. But both of those metals are pretty soft and can be worn or scratched through. And the copper under the nickel is very susceptible to copper solvents.
Once you've got it cleaned up, use a silicone cloth once in awhile over the whole surface for protection. And don't let cleaning solvents sit on the surface for any length of time.
-Don