You're right, video output is very low at 640x480 ppi. If you follow one
rule of thumb (that you grab enough pixels that'll provide 300ppi at the
FINAL desired negative size) you can see that you're going to end up with
a very tiny image! That's not to say that the textural,pixelated look
doesn't have it's own charm; I'm just passing on info that will provide a
true, "traditional" photographic look. "Real World Scanning and
Halftones" claims that with a video capture card on a Mac or PC, you can
get better quality than the cheapest digital cameras. You can use that as
a sort of guide for what to expect.
About slides from digital files: Film Recorders are rated by how many
lines they "write" onto the slide film. If the film recorder writes 4,000
lines across the long dimension, it's called a "4K" resolution model.
They go higher than that (8K, 16K), but I don't think you'll witness that
"true photographic" look at the resolution (1.7K) you mentioned. (Some of
the lower end film recorders are really made for presentation slides; you
know, the kind that the vice president of marketing uses to show slides
of "sales this quarter.")
Again, the above specs are for "good" photographic output. Since you are
enjoying the rough and grainy look, you should certainly feel free to
break all the rules and see what happens. Besides, gum isn't exactly
known as a process that holds fine detail.