PARI is more a place to go to learn things as apposed to see things. It is better to go to their event calendar and find a day to visit when something is actually happening at the facility.
A quote from their website:
PARI’s mission is to provide hands-on educational and research opportunities for a broad cross-section of users in science, technology, engineering and math (STEM) disciplines. Scientific instruments at PARI include two 26m (85ft) radio telescopes, a 12.2m (40ft) radio telescope, a 4.6m (15ft) radio telescope (dubbed “Smiley” and operated remotely by students and teachers), a high frequency Jupiter-Io/Solar antenna, 11 optical telescopes on the PARI Optical Ridge, five weather and atmospheric monitoring stations, and various environmental monitoring and measuring instruments. All of these instruments are used students, teachers and volunteers of all ages, making PARI one of the few places in the country where world-class instruments are not restricted to limited use by top scientists. At PARI, students learn by doing, which makes it a very rare and valuable resource for students and teachers alike.
Inside the Cline Administration Building is a small exhibit with historical items. There is also a nice collection of meteorites, gems, and minerals.
Outside there are a few hiking trails. Be sure to checkout the Parks Observation Deck where you can get a good view of all the radio telescopes and satellite antennas.
The Pisgah Astronomical Research Institute continues to expand its offerings. They were building a new cafeteria the day we visited and work on the hiking trails is ongoing. It's a nice place to stop even if just for the view at the observation deck.