They aren't intuitive molds, in the system-1 sense; 'particle' and 'wave' are theoretical constructs

I think that is pretty much the wrong way round. The only way you can model a dimensionless particle in QM is as a diract delta function, but they are mathematically intractible (with a parallel argument applying to pure waves), so in a sens there are no particles or waves in QM, and whatever w/p dualism is, it is not a dualism of sharply defined opposites, as would be implied by Bohr's yin-yang symbol!

. But in fact I seem to either see spin-up or spin-down, not both.

In fact, you see macroscopic pointer readings. That is an important point, since Many Worlders think that the superposition disappers with macroscopic decoehrence.