Wuppertal is essentially an industrial town, so there's not really a lot to see there other than the Schwebebahn. There's some old architecture, but a lot of it is newer build. I went to Wuppertal I think four times during the two years I lived in Germany, all of them because I had a meeting at one of our sites there. Cologne, on the other hand, I visited frequently to be a tourist.

However, if you are into archeology and paleoanthropology, the Neanderthal skeleton was discovered not far from Wuppertal and there is quite a well-done museum very close to the site, outside of Mettmann. If you have an afternoon to spare, it's worth thinking about.