I agree with more time in Krakow. Much to see, flavor to soak up, from the old market square, which is huge, the very different churches (St. Mary's, the Dominican and Fransiscan churches, Pope JPII's haunts, the old wall, the jewish quarter, even Nowa Huta and the church there are worth a visit, though not necessarily on a 3 day visit. The underground jazz clubs, vodka and apple juice, great restaurants at good prices, make for a nice time.

I have several friends who have enjoyed the salt mines, but I haven't. The trip to Auschwitz seemed to take more than an hour, but my memory may be hazy.

Have a good time.