Yes, i feel you need to periodize. Your body, needs a change everyonce in a while. The amount of time I spend periodizing, revolves around my goals, and wether or not i am training for an event.
I don't follow a traditional periodization model, but after every three or four weeks of steady training, I'll reduce my overall training volume(sets and reps not weight) for a week and this has been invaluable in keeping me from burning out.