As soon as I quit the Finder, the installing process went from a crawl to a dash, and completed in less than half the time I'd expected. I have not duplicated this, as I have nothing else from SoftwareUpdate to install. But it seemed to make a marked difference in the optimization speed of Apple's updates and installs. Hope it works for others too.
[Editor's note: It should be possible to do some timing comparisons using the Terminal's "sudo update prebinding" command to verify these results. Run it once with the Finder running and again without the Finder running and time each trial. Or if you like living on the edge, try the above yourself and comment back regarding whether you saw a notable speed increase or not. I have done neither of these things, so this hint is clearly both experimental and unverified! Proceed at your own risk if you decide to test it yourself...]

