People are more willing to talk with you if you have a referral, and they're much more willing to hire you and trust you if you've worked with people they know. Paprocki says that the right referral could make a difference. But they would have to do the marketing themselves. One of the biggest problems with photographers marketing themselves is they don't call people. They expect people to call them.
Photographers can be the worst marketers in the world.
In the end, keeping an established client satisfied is very simple, treat them well and keep the quality of your work high. They don't care about the location of your studio, how it's furnished, or the lunch spread you provide. They do care that doing business with you is hassle free, that you can be trusted to deliver as promised, and the final result is something they'd be proud to enter in a show, or place in their own portfolio. You can end up doing things that don't make you feel good about yourself in the long run. The best thing to do is just make your work as good as possible and be reasonable without going over the line of established business practices.