I've seen a lot of differing opinions on this and I wanted to ask here - what are your thoughts on running-wheels for pet rats? We've got so many chew toys and hidey-huts and perches and hammocks in their cage right now that there's no room for a wheel. They get so much exercise running around and climbing in there - plus we play find-the-shredded-paper-towel game with them several times a day ...we'd be happy to add a wheel to our free-range sessions, but do people here think they are an absolutely necessary cage accessory?