Basically, you are telling me that Krakow is a nice city worth a visit for one week or so, but can be boring for a long stay ?
Don't listen to them. One of them is trolling under endless guest names, the other is known to sneer at everything in Poland.
Krakow is perfectly fine if you enjoyed Warsaw. It's much the same to be honest, except a bit smaller - if you're looking for a city that is attracting a lot of foreigners and has a soul, Krakow is it. Wroclaw is another option, although it looks wrecked architecturally in many places.