I don't wash my bike very often anymore, but it should be done at least once in a while. Buildup of crud (especially if you live in a place with salt, either from the ocean or the roads) can be corrosive and damage your bike. Also, a wash is a good way to look over your bike and check for loose, worn, or damaged parts, and to catch leaks (oil, coolant, fork seals, brake and clutch lines, as applicable) before they get serious. All of that applies to safe operation of your machine, as well as having it last well, which then does apply to your riding pleasure. You can't have much fun riding a bike that is broken down or has crashed.
2 bikes i haven't washed since school ended 4 me and the other i'm a fanatic about specs of dust. Depends on the bike but then again the tillie only comes out half a dozen times a month. The other bikes i ride the piss outta maintain religously but don't really wash em.
I think I may have washed mine in... early June maybe? If it looks real bad I'll give it a quick rubdown, but I probably won't clean it like it should be until winter hits. Then it'll get a nice fairings-off polish and inspection, but that's it.
I wash mine when the black frame isn't shiny anymore. The tank gets wiped down once every other ride atleast. Rims are cleaned once every month or every other washing depending on riding and dirtiness. My bike is worth less than 1k, but doesn't mean I can't love it and keep it in tip top shape