This has made me see the error of my ways: what the hell was I thinking, trying to store things that I care about on little plastic discs? Haven't I learned this lesson many times over already? Why yes. Yes, I have. I should have been storing them as normal files in my well-backed-up home directory all along, just like I do with music.
So of course I didn't save the original intermediate files, and find myself re-ripping from the DVDs I burned. (Well, I still have the VHS tapes, but I doubt I'm going to lose any perceptible quality by ripping from the DVDs, and that's faster).
What's the difference between MPEG4 and H.264? The files that Handbrake writes seem to be the same size (around 7MB/minute), but the Quicktime Player interface seems more responsive when playing H.264 than MPEG4.
I suppose it would be pointless to save the video at any resolution higher than 320×240, given the source material? Or might that lose detail, given how many trips through the encoding ringer they've made now?