Depends where you are flying. I certainly wouldn't do it after every flight, and generally just give mine a wipedown with a damp cloth whenever I notice it's looking a little grubby, but every now and again I'll use a proper cleaning wipe - never any need for more than that. However, I might make a point of doing so if I've been flying through - say - an industrial area where there were a lot of airbourne pollutants (power stations and refineries at night can be incredibly photogenic, local laws regarding photographing them permitting).