I have several Buddleia's in the garden ranging from pink, lilac through to dark purple, at the moment they are in full swing, together with attendant butterflies and bees. Although they are considered a weed as they self-seed everywhere on waste ground and railway embankments, they are, in my opinion, a great addition to the garden for the wildlife they attract. Once the flowers are over they do look a bit of a mess with all the flower racemes turning brown, but with a bit of judicial pruning they give a second showing of lesser blooms which prolong their usefulness in the garden. Alas the season for them is all too short. To keep the blooms lower down on the bush so as to be appreciated they must be cut hard back in spring.
Just as an afterthought, if you want to increase your stock of these lovely shrubs, just propagate by taking a hardwood cuttings in autumn, and literally just stick it into the ground.