Leave the points as they are. The chance of there actually being 28 cars on the grid is small. Firstly BMW or Sauber or whaterver-they'll-be-called have to be let in by the other teams (I thought there wasn't enough garage space for more than 12 teams and now we've got 14?).
Secondly, some of these new teams still sound dodgy. I'd be very surprised if they all make it to the grid, let alone through the entire season. Giving points down to 10th might sound OK with 28 cars but as the numbers dwindle back towards 20, and they will, it doesn't sound quite so good.
You also have to factor in that Renault are about to be bent over from behind by Pat Symmonds and may not survive Crashgate. One less team already and Toyota looking rather precarious.
Leave the points alone I say.