How can I speed up batch RAW processing in Aperture 3?

I do a first quick pass looking for anything decent, even stuff that looks bad but can be possibly saved - I rate this all as one star.

Then I work through those, quickly flipping through them and editing anything that interests me. Those I rate as two.

After that I review all of the two stars and see if there's anything that really stands out, that is worthy of more attention - those I rate as three or higher depending on what I got.

I do sometimes lift and stamp changes, mostly around white balance and metadata (don't forget to add yourself as the creator and a copyright notice to all images if you didn't do it at import!). Sharpening I tend to like to only add to specific areas, if at all.

I have also had Viveza 2 and the other Nik products for a while but only recently started using that more. A separate tip for that is that I like to use Viveza 2 first to alter tones in an image (spotlight certain things, fill or darken areas as needed). Then I duplicate that version and use ColorEFX and/or Nik Sharpening (SharpenPro) against the duplicate version, so I have three masters when I'm all done - but since you can't undo ColorEFX and SharpenPro, I like to have the "clean" Viveza image there to re-work from as a base (and that will also work out well if you need to upsample for larger prints and thus have to re-sharpen). I also like to append to the second and third created master version names with the tool that helped to edit them (-VZ for Viveza, -CFX for ColorFX) but that might be placed better elsewhere since export to Flickr will change your version names.

ADDITION:

I'm adding one more thing. Go back into your photos a week or so later, and do one pass through. Especially if you have a lot of photos you can start to get more and more critical, or perhaps single-minded... in any case it always seems like looking back through images later one, I find at least one that I really love that makes me wonder why I left it down in the low-rating dungeon.