I took a class today from an instructor that clearly was neither a cyclist and nor much of a spin instructor. She was out of breathe most of the time. Her class was interesting. She did alot of slow climbing/grinding. I don't recall any spinning at all. This is suppose to be an aerobics class. If I want to do anaerobic exercises I would go lift weights. So I just did my own thing. I got into a good spin, with adequate tension to simulate a slight breeze and only occasionally got out of the saddle. I know what my body needs and I don't have to prove myself to anyone in the class, least of not the instructor.

Bottom line, be sensible about spinning. Some things make sense and to cyclist, some don't. If you don't otherwise ride, then by all means, do the "stand up, sit-down, fight, fight, fight..." moves but always try to stay aerobic.