Our group of 4 people are going from Wroclaw to Krakow for a weekend.
4 people, you might as well drive. The only problem is the toll barriers at Bielany, Gliwice and between Katowice-Krakow. But it's not tourist season, so it should be clear.
Having said that, the 3 hour IC connection between Wroclaw-Krakow is very attractive.