I lift year round as I believe that the balance between cycling, hiking, weight lifting and core exercises is really important. The weight lifting, in particular, helps maintain bone density. I only lift twice a week, if I can squeeze a third one in, great, but I don't kill myself.
The core exercises with the ball and bands I do once to twice a week. When I am riding high mileage its really tough to do a second one, as the bands really wear my legs out! But my PT guy said that you can stay strong with a once a week regimen.
I've been lifting weights since I was 17, I'm 49 now, and have maintained really good muscularity (they say we start losing it after 30, bully to that!)
I think to a balance between exercise is important as IT band issues plague many athletes. Keeping those stabilizing muscles strong is really important.