I sent out 1700 post cards this spring EDDM. The printing company I went through was pretty dishonest. They failed to mention that the cost of shipping was not mentioned in the price even though I asked how much it cost for everything. Make sure you know all the costs associated with what you're doing before you have boxes of post cards sitting in front of you and you're told you still owe 500 bucks. The whole process was more difficult and annoying than I expected.
From sending out 1700 to what I considered my ideal client base these are my results:
1. A one time job spraying weeds and dandelions.
2. A quote for an old guy that thought I was satan quoting him $25/week for mowing.
3. 2-3 new weekly mowing clients.
From my experience I paid roughly 300 dollars per weekly client. If I had plenty of money and a strong desire to grow that might be worth it, but frankly I have received 20 new clients this year just from having a website and a good web presence. It's pretty tough to justify for me.