Cardio is nice no mather how you do it...
Personally i use the tredmill every day i go to gym even if after i am pumping iron ... EVERY DAY!
Runnning 10-14km with 10km/h speed....always having a nice breakfast filled with carbs and pre-work coffeine pills before...cause if not i crash at the running and have no energy to lift anything after that...
For me i did wonders...but hey...each one with its own way..