I'd say no. I don't think people who get 570 are necessarily better than people who get 500 at A level. Certainly I've not seen this happen when it comes to grades. A levels at that level are about jumping through hoops, and I think an A* grade would just reflect that, not any inate benefit.
I'm also against post-A level applications, as I think Oxbridge are right in looking for potential and motivation above all. Someone who's amazing at the interviews, who can form a logical argument about a problem they've never studied, is likely to do far better than someone who can memorise facts easily and has been taught to jump through hoops.
IMHO, the interview process works, and as in any competitive situation, with universities competing for the best students, Oxbridge has all the incentive to try new things to better choose the best students. Oxbridge admission isn't anywhere near as much a lottery as LSE, UCL or Warwicks for many courses, who have more applicants per place and don't interview.