Hi John,
I use someone in the same field as your client.
To the best of my knowledge he (my guy) doesn't have a newsletter, although the first time I went I'm sure someone either purchased or was given a copy of an in-house magazine. I might be wrong, but I'll check it out and see what the deal is with it.
Getting more out of clients is the natural thing to look at and if you have multiple referral programs in place that may tip the balance. From what I can gather from the figures you provide it looks like your customer lifetime value warrants such a strategy.
However, I think you "hit the nail on the head" when you mentioned that getting those that aren't sick to come in, even for a preventative check-up, is tough. Growing your list and getting to those that are in
immediate need might be a more effective option.
The guy I use previously had regular slots on prime-time morning TV and continues to do regional radio programs on BBC Radio. See link below (you'll need to scroll down to see the radio slots scheduled)
Jan de Vries Healthcare Ltd
Could Dr. Proctor get a slot on some local radio stations and conduct a health clinic phone in? I'm sure many stations would love to have him on the air.
Possibly, try and dedicate the phone in to something unconventional but entertaining like "embarassing illnesses". Many people either have an embarassing illness or know someone who has one e.g. flatulance, piles etc.
During the program you could urge people to pick up a newsletter dedicated to the topic of the radio program, or encourage listeners to come in for a free consultaion on a specific day.
When he's scheduled to appear he can put this in his newsletters and tell his clients when he's on air. This should go down well with readers (extra social proof).
Overall, I think it might be easier in this case to try and expand the list through new channels e.g. radio, rather than contiuing to mail the less responsive.
Although, measuring the progress of the referral program should tell if it's worth pursuing with the mailings.
Congratulations on getting so many patients back with the newsletter!
Best Wishes,
Tom
P.S. If you want to ask me any more questions, please feel free. I hope what I've said is helpful to you.