MDE has its share of things to do, mainly visiting neighboring Paisa towns. My plan for the next time there is to do that, perhaps also fly down to Nuqui beach which is conveniently accessed from MDE. For the sheer number of things "to do" nothing compares in Colombia with Bogota.
Also, what exactly do you do for fun when not in Medellin? What is there to do for fun in Cali that can't be done in Medellin?