Yes, you've got to 'tout' for business; the folk world is full of reasonably talented performers sitting waiting for the knock on the door, for the majority it just doesn't happen!
I've some experience from both sides of the question, as 'an agency' and currently a folk club and festival organiser. Like Joan from Wigan, my festival, The Flanders Experience, doesn't book people to perform but I still get deluged with CD's. I can't complain, as the Festival is a member of, and listed in the Association of Festival Organisers mailing list. I have a standard reply that I send to applicants explaining the festival basis.
As a folk club organiser the situation is different and I can only emphasise the point made earlier, that presentation is everything. The range in standard of material that comes through the letterbox is amazing. I've had a tape, no case, with a (badly) sellotaped label that the would be performer had recorded at a live session in a busy pub. The best presentation, from the USA, was a well-produced CD in a very plush folder containing biog details and copious reviews of live performances. I didn't book either aspirant, the former for obvious reasons or the latter because they would have 'died' at our strongly traditionally orientated club.
Some performers and agents have a very screwed view of the folk world and get quite ratty when I don't immediately jump at the chance of making a booking. The simple facts are that at Herga we book one guest a month, that's twelve a year, which isn't many when you can get three or four requests a week. The club members vote each year on a wish list of performers that they have suggested they would like to see at the club. At least three quarters of the slots are filled from that wish list, so the dozens of hopefuls are actually competing for just two or three places. I tend to book between six months and a year ahead, so the phone calls and e-mails from performers sorting out a tour in the near future have no chance.
That's a long-winded way of saying, make it as good as you can but don't expect a massive response. In the last three years I have booked just one performer on the basis of their CD and that was as much due to the recommendation of a club member, another 'catter,' who had seen them perform and whose assessment I trust.
From the point of view of an Agent, keep at it, phone to see if a demo material would be appreciated, send it promptly and follow up at a sensible time after you've sent the package. Keep accurate records of all your approaches, you'll quickly lose track of all the contacts you have to make. And finally, grow a very thick skin, you'll need it.
(For 'Hovering' read 'waffling,' sorry!)