Cadence is simply pedal speed or crank RPM. It is very important and incidentally something you DO want on your computer. Cadence is not only key to fitness but power generation as well. Its like being in a particular power band with your car as you are effectively the engine. There is a balance between torque and horsepower and you want to strike this while you ride by being in the proper gear relative to the amount of load you have be it into a stiff head wind on the flats or up a 5% grade. As to your computer, I would take it back because you do want cadence...I believe the centerpiece of a bike computer. The other thing is wireless computers can be sketchy in performance. Some will weigh in and claim they have had no issues but others have. If Karl falls through on buying my new Astrale 8 I got as a present, I will sell it to you for half what you paid for your cordless Cateye without cadence if interested.
HTH,
George