Plan versus random workouts

Hi there, just wondering what people’s experience is of following plan versus random workouts? I ride about 6 hours a week pretty consistently but I just pick a workout based on mood - usually shorter interval sessions like Baird/Jobs or overs/unders because I enjoy the variation. I am thinking about starting a plan because I’m keen to progress (and i’ve started to plateau) but the workouts look more dull in the plans so i only want to do it if it will generate better results. thanks in advance.