Personally, I think if you are selective and you are ranked less that 100, that's pretty shameful. Your school has the ability to select the brightest group of kids and you get beaten by Comprehensive schools (Public, Catholic and Private Comprehensive).
As for bonnyrigg,prairiewood and maroubra, that's stupid. Those schools are ranked in the 300s - 400s. If they were to make more selective schools, at least give it to the schools who deserve it - Homebush Boys, Burwood Girls High School Strathfield Girls, Canley Vale High - at least those schools are ranked in the Top 200.
I don't think it will affect the school's in the local area, because they'll still only have 200 spots or so, so the leftovers would still have to go to the surrounding schools. My school's in that area (Patrician Brothers' College, Fairfield) and i don't think we'll be affected too much if it does happen.