To me cadence is everything. The cadence number fills the top half of my Garmin 305 screen. It is the one number I always want to know. That being said, there is no right, and no natural cadence. Cadence is a choice. What I was get at before was an old training trick. If you can breath but your legs get tired you are mashing too low. If your legs are fine but you're all out of breath, you're spinning too fast. If you're out of breath and out of legs you've just did one too many intervals.
If you ride a fixie over rolling terrain there is no way to keep a constant cadence, you'll mash up hills, spin down the hills and cruise on the flats, and all that is ok. But most of us are not on fixie's, we ride gears. The gears are there so you can ride a constant cadence. Most of the time for me that's in the mid 80's, but not always. Sometiems I'll ride my road bike like a fixie and let the terrain dictate what RPM I spin.