We were in Vancouver (for the first time) in September and I'd highly recommend staying over night. We stayed at the Sheraton Wall Center and really enjoyed it (only if you're not afraid of heights). The views from the higher floors are spectacular. Take the afternoon and go to Stanley Park. They have a wonderful aquarium and beautiful gardens. Downtown offers a lot if you're into people watching. I would imagine it's especially fun for teenagers, since it's the hub of the University of BC.