Is it worth it to get a bike computer with cadence? I'm looking into purchasing a bike computer, primarily to track distance and speed. Is it worth it to go up a notch and get a computer that also tracks cadence? How accurate are bike computers at doing this? I'm not interested in wireless computers - I hear too much about interference, and they are much more expensive (thus targets for thieves) -- so is it worth it to hook up more cables to the bike in order to get cadence info?
I also think the answer is "it depends", but for slightly different reasons to Daniel. I think it depends on why you're cycling.

If you are training, then measuring cadence can definitely be useful. In fact, there are training programmes that are based around cadence. (You're basically looking for a high value, and a steady value.) 

Otherwise, the information has more-or-less interest value only, although you could still argue that the "steady" side of the value could be used just to improve your technique.

As regards accuracy, cadence is measured using a magnet, just like speed and distance. So there's no reason why cadence should be any less accurate than speed and distance. It depends on the hardware of course but I'd expect computers these days to be pretty accurate.

As regards your reservations regarding wireless technology, again its going to depend on hardware but wireless is the way all the high-end computers have gone, so there is certainly not any inherent problem with this technology. It is possible to measure things like speed, cadence, power and heart rate, even I believe gearing info, all simultaneously, all wirelessly and without interference.