Salt mines are definitely worth a visit. Take a bottle of water though as the salt in the air makes you really thirsty. Try to go as early or as late as you can, because at peak times it can take forever to get out (there's only a tiny lift that takes about 4 people so the queue can be a long wait).
The Schindler Factory is definitely worth a visit.
I always stay in Kazimierz, the old Jewish ghetto and where the pogroms were - it's my favourite area as there's loads of alleyways to explore, and often you'll reach the end of what appears to be somewhere going nowhere only to find a small square with restaurants and bars. Some areas are quite haunting - there's a bar I use with a courtyard and on the walls of the courtyard you can still see bullet holes. For context Kazimierz is about a 15 minute walk from Rynek Glowny, the main square.
Krakow is one of my favourite European cities - I love the architecture, the small winding streets, the abundance of bars and restaurants, the prices when you're there, and the fact for the most part it is a very walkable city.
Great place.