Yeah, don't spend the extra $$ on the wireless function. Put that towards something else like a new set of gloves or grips, lube etc.
Also, seeing as this is the MTB forum, I assume its going on your MTB. But, where do you ride your MTB. Is it used only off-road, on-road, is it your only bike, or do you have another bike to train on?
Reason I ask is that if you mainly use the mtb off-road (80%+), then a cadence counter isn't neccessary as the terrain changes that often, going from tight singletrack descending where you're unlikely to be pedalling, straight into a short-steep technical climb. Put the extra money towards something else too.
However, if you train on the mtb on the road, then yes, I would probably get one with cadence if you can afford it, as it is much easier to monitor and maintain cadence on the road.
HTH.