Hey, I can't see this approach working for long, it's exactly the kind of thing they are trying to cut down on. Like you say, it should not hurt the main page but it would be interesting to see if the mini sites have taken a hit as they are essentially low quality, cookie cutter garbage created just for the search engines.
I am unsure how google handles frames as it is not technically duplicate content, it is just a window to the main site itself but it is kind of manipulative to present one sites content in another one, especially when that other one is a page designed purely for search engine traffic and with identical content (bar the location keyword) to a bunch of others.
This whole approach is flawed.