all hail paul!
the wow works now, thanks entirely to paul's gentle noodging. his suggestion was that i lower the needle bar even farther, so that it plunged as deeply into the bobbin case as possible without actually scraping metal. that has done the trick, and my stitch quality is as good as can be expected with a spacker like me behind the wheel.
last night i did a row of a fairly detailed pantograph. it looks good! the only places there were skipped stitches were in spots where i knew i was moving the machine too fast, even as i did it.
all hail paul!