And..... (sorry to go on).....
Be sure to track your customers / enquiries / leaflets well. If you can point out on a map which area's got you first leads or enquiries, then which of those turned into customers, then which of those gave you the most profit or more customers or whatever you can try and work out what type of area's they are (what type of homeowner) and then find other similar area's.
You'll find county's that are hundreds of miles apart will still have the same types of area's and therefore common patterns in their lifestyle and spending.
Doing a leaflet drop in stages and collating the information for each 'run' will help you point out the right direction to go for your next spending on leaflets.