Yes, the plant would look better without those old stems. If the new growth has excess distance between nodes, a bit more light will help. Kind of a gangly, leaning plant by nature. If it stays upright and blooms in the fall, it's happy. To encourage branching in general, for this or any branching plant, assuming it's not in insufficient light, removing the older leaves at the base of the stem will encouraging branching. Pinching the tip will usually cause the tip to bifurcate.
