Great comments, everyone -- thanks for the kind words! As I begin to focus on learning to use these machines, acquiring them for specific purposes is all I'm interested in anymore. It's as if I needed to get this out of my system. I remember reading about the process of acquisition and how buying more of a less expensive item doesn't sate our psychic appetites but that collecting (hunting and gathering) is hard-wired.
Yeah, the 30 came out OK. (Those overhead halogen lights reveal every single flaw in the finish and every particle of dust. It actually looks better in more natural lighting.) Since this one's condition is not as nice as my other 30 (which is near-mint), I'll sew with it if I keep it.
And I completely agree about being cautious re. selling off stuff that right now seems like stuff that's in the way. I was excited to find this Pfaff and I have to remember why: they're not offered for sale all that often (in this neck of the woods). For myself, regretting buying a something I don't value is much less than the regret of selling something I do.
As for the non-metal gears in the 130, there are actually two: one that works off the main drive shaft and controls the zig-zag function (so the straight stitch 30 wouldn't have this gear) and a small gear off the hook's shaft. (I'm not exactly sure why plastic/nylon would have been preferable other than weight; the differences in cost were, in the 1950s, probably negligible.) Another non-metal part is the cleated belt that drives the lower shaft (the same design featured in the Singer swing series). The 30 doesn't have this belt, either.