An ADF may not be used in an airway, but it is easiest and most available means of getting from the airway to the airfield without RNAV or GPS, so I don't think they are without use. The need for an ADF in a typically equiped Cirrus is, as usual, another matter.
Sorry for the thread tangent, but as a GPS dunce I've wondered if units like the GNS430 have phantom VOR style RNAV capability. This would surely serve the same purpose as an NDB but with GPS and VORs confirming each other's accuracy?