OK, I know this is tangential, but after seeing a couple of you mention it I had to remark:
Do not judge whether your weight is healthy by your BMI alone.
The BMI scale is accurate only for people that have a particular bone weight, muscle %, etc. I'm not underweight according to BMI but after a recent (unintentional) weight loss you can count the ribs on my body and my blood pressure has dropped so low that I need to take electrolytes or risk passing out. Am I happy with this because BMI tells me I'm a good girl? Uh, no.
All that said, I'm not trying to say that you guys are being irrational or something; ultimately it's a personal preference, you need to judge "healthy" based on where your body is most able and feels the best, and it sounds like most or all of you are thinking of that somewhat. Just don't get suckered into believing that your ideal weight is determined by a mathematical formula.
OK, now that I've blabbed...
I have "weight issues" due to illness, but surprisingly, neither overweight nor underweight (I've been both) seems to affect my DDR endurance until I get down below about 160 pounds. Being lighter does make it somewhat easier for me to recover from mistakes, though.
If you really want to improve your stamina for DDR do rowing (either join a rowing club or just join a gym that has one of the machines). It helps build cardio and leg strength, but is easier to get into than, say, running; it helped my DDR endurance tremendously when I did it.