DTV already has ILSs at both ends with two alternative procedures if the ILS is out of action. The number of times a CAT II decision height would get the aircraft in where CAT I wouldn't will be infinitesimal.
On that basis no airline would change their decision-making on whether to operate to DTV on the basis of, at most, a handful of days a year.
As regards CAT III, that's just cloud-cuckoo land. You'd have to be seriously in the market for high-frequency flights by airlines that have CAT III capability before that would look remotely attractive - Eastern? I don't think so. KLM F70s? Maybe, don't know. Bucket and spade charters? Forget it.
DTV is already an extremely well-equipped airport. The facilities aren't the problem. It's the demand.
NS