The "new" system will solve most of these problems. Location will be a requirement, it was also have additional fields to supply information such as:
price
phone number
best way to contact - phone, email, or pm
best time to contact
Because I am going to force location, I am also looking at away to display on the classifieds on a google map. It would be real easy to scan all the classifieds and see what is in range for you. The hiccup on this is finding a good, free, geocoder. I have to convert zip codes into lat, long. I will also display the location on the classified listing page, so you wont actually have to open a thread to see where it is located.
I don't have a solution to weed out tire kickers, nature of the beast. But, I am willing to listen to any ideas.