As a former instructor (aerobics, stretch, back in the olden days), I have found that there's basically 2 kinds of spin instructors: Aerobics instructors who are on a bike and cyclists who teach spin. While there are some of type #1 who do safe and fun classes, those are the ones who I find doing the "push ups on the bar" and running in place at very high cadences. Don't feel compelled to do what they do. I find that no one says anything to me if I do a seated climb while they are standing and running like crazy or I am standing and going at a lower cadence.
I like the group aspect of exercise once in awhile, but not like I used to; I also like working out to music. If you can find the instructor that is right for you, make it more of your own work out. Usually every gym has at least one person who is a roadie or a tri-athlete who teaches spin. Those are the ones to find.