What you have is 1986 Nishiki Prestige. The rear derailleur is circa 1988-1991. It looks like Athena but could also be Xenon stripped of it's painted finish, which might be why the Campagnolo logo is missing from the parallelogram. The front derailleur is the OEM SunTour Cyclone.

Going to a 9 speed would require cold setting the rear triangle to 130mm. This is not a big deal. However, I'm not sure if you just want more gears but also wider gears. If it's the latter, another alternative would be a triple crankset.