Games That Raise the Heart Rate
The Rocky Mountain News is running an article by Kotaku's Brian Crecente entitled Fit to Play, about the effect that games with a workout component have on the health of the player. From the article: "...five years later and 100 pounds lighter, Jennsen is a video evangelist in the most 21st-century sense of the word, preaching the fat-melting, muscle-building power of video games to generations that have grown up holding joysticks."
I agree with a lot of what you said. I do think part , or most, of the problem is more related to the fact that exercise is hard rather than boredom. It becomes much easier over time and less "boring." No matter the exercise.
I love playing DDR (actually StepMania) for hours at a time though. I have those fancy RedOctane pads and they do work well. However, I ended up building my own hard pads that I could wear shoes on. You really need shoes to protect your shins and ankles (shin splints hurt). I still alternate between the soft and hard pads depending on my mood, but I use the hard pads with shoes most of the time because it lets me play longer without damaging anything (I also run and left weights).
The ratio of people to cake is too big
I'll tell you, this is a place I would attend daily. DDR is great fun - I've gotten so into it that I built my own studio, but doing it alone isn't as much fun as I'd imagine a health club setting.