Yeah, I don't have any idea how a spin class can help your racing. I try to spin once or twice in the middle of the week, Tuesdays and/or Thursdays to be precise. I also try and stay in the back and do my own thing most of the time (ie work on things I want to work on, like smoothness of pedal stroke, leg speed, one-legged drills, extensive out of saddle riding etc).

What I have noticed is increased out-of-saddle riding and overall stamina, leg strength and weight control. Of course, I'll rather ride outside, but since I don't ride at night, it is another arrow in my quiver for after work exercise . As somebody pointed out, it is what it is, and what you can make out of it.