My most useless, frivolous, just-don't-go-there wish is a fancy sports physiology lab profile - VO2max, lactate threshold, DEXA scan for both bone mineral density and body fat measurement, accurately measured cycling power profile - and a customised training plan. I'm in my fifties, I enjoy sport but have absolutely no talent for it, and after all these years I have a good feel for what works for me and a bunch of numbers wouldn't turn me into an Olympian or even an international-standard Masters athlete so it's better that I save the cost towards ...
The stupidest thing on my wish-list is a fully suspended, custom built, mountain bike tandem. One of those machines that costs a five-figure sum to build and has the same sort of upkeep costs as a thoroughbred racehorse. My husband and I love road tandeming, and being able to ride rough off-road terrain on a really good bike seems like the obvious next addition to our repertoire. But the reality is "so many bikes, so little time". We're practising delayed gratification. If we still really, really, really want one when we actually retire and have lots of time to go out to play on it, we'll have one.