That extra work does help. Try this as well, its a technique that I learned from Chuck Violand.
Go through your business area and look for buildings with these characteristics:
Paved parking area
A sign on the building
Landscaping and shrubbery
(All say "I care about appearance")
Go in the building, and if the carpet is heavily soiled, leave. (If they let it look bad before they clean, they'll definately be "low bidder types" who expect too much.) If the carpet is clean, or nearly so, they probably pay to have it cleaned regularly, or its relatively new. And its unlikely to have been abused and full of residue.
Once you establish that they "qualify for you", approach the receptionist and ask for the name of the decision maker, not for a cold sales call,but just so you can mail "them" important information about carpet maintenance. (In a number of places, the "gatekeeper" actually makes the cleaning calls. Imagine a doctor or lawyer shopping for carpet cleanign). Because of the non-threatening approach, she'll either give you a chance to make a proposal to her, or give you the contacts name gladly.
Go back to the office/your home, and mail your information directly to the decision maker, and mention in the letter that you will call on a specific date.
When you call and the receptionist/gatekeeper answers, you'll know her name, mention the reason for the call, and your more likely to get through.
Once you get through, get an appointment to give them a proposal.
This is a bit more involved that direct mail, but you'll get a far higher percentage of interviews to a far better prospect list.
I hope this helps!