Personally, I don't think there is a lot to see in Osaka... there is the Osaka Castle, Universal Studios, Osaka Aquarium and Dotonbori/Shinsaibashi, Umeda Sky Tower. My personal highlight for Osaka was the aquarium.

As it's only 30 minutes from Kyoto, you can consider it as a day trip from Kyoto instead? Although as a day trip out of Kyoto, between Osaka and Nara, I would choose Nara for you since you mentioned that you are more into culture (Nara has 3 World Heritage Sites), rather than nightlife (one of the highlights of Osaka)