In my line of work (Fujitsu) I have replaced many faded VFD units, both Noritake and Futaba. A primary factor in VFD fading occurs when a heater/cathode wire that streatches across the front of the display elements breaks. As Mike indicated above, durability is not a VFD strong point since a mechanical shock will easily break these wires.
Another problem I encounter with Noritake units are poorly mounted SMD transformers which "dismount" randomly, shutting the display off. Remounting does not revive the display, probably because of a current spike caused by the dismounting transformer.
I do like using the VFD units in non-battery applications, though, since they normally come with serial and parallel interfaces and are much easier to use.

Hal