1% of 1000 is 10 not 1.
Lets just think about junk mail here. I hate to say it but that is what your post card is. You have but a fraction of a second to catch a potential customers attention before your post card hits the trash.
Your design is very critical and you had better be offering something very lucrative to get a second glance.
I personally think door hangers are a better way to market to an area. I have seen people take the door hangers off their doors and typically they spend a few seconds reading it. Which would you spend more time looking at something stuck to your door or a piece of junk mail? But response rates I have seen posted here on LS state about the same response rate for both.