The answer is YES! Your prior clients are your best referral sources. When you do a good job for them, they want to sing your name out to anyone they know who is looking for a home inspector. But, if you don't stay in touch with them, after some time, they will forget you, even if you did a Spectacular Job!
So stay in front of your prior clients with some sort of consistent email newsletter. The Savvy Inspector has a Great program that is almost like, Set It and Forget It!