Ian, I used to be in a franchise and many colleagues tried directories for The Fire Service, local hospitals, this, that and the other and while they all promised "a massive boost to your business" or similar cobblers, none of them ever gave a worthwhile return.
I very much doubt if the position has changed, if they were such a great success the plumbers, roofers, joiners, builders, glaziers, driving instructors and all the other local businessmen and women we all know would be raving about them.
Same with charity/volunteer etc directories, why give £100 - £200 a year to get in a directory which brings in nothing for you and 60% of the money to the directory producer. Give the money straight to the organisation and see a far greater % of the money used in the local community.
Here endeth today's sermon!
Edit: 3.30 pm and just had one on the phone supposedly from the Fire Brigade! Before he could start, "No thanks I don't want to go in your directory", the b****** hung up without another word.