I've never tried door to door and do my marketing mostly through targeted mailing(also have web site and trucks lettered). We are not a huge company and I do all apps myself.
We still like to step on the lawn for estimates but have given quotes over the phone ---- gave high end quote with disclaimer about ease of application.
One idea may be to do a cluster of door to door sales when you are asked to give an estimate. You are already there so no extra drive time and it's always nice to have a stop with 3-4 homes side by side.