[Arran]

 I believe that brand Z used to acquire speakers from an outside speaker manufacturer like Utah or Lansing (though I can't remember which) so that would make a difference in sound quality. As for the build quality, the most obvious example of corner cutting is in the power transformers. As for the shutterdials, whilst somewhat interesting in the end it's still a black and white painted tin dial, even the big black back lit dials before them were just a back lit piece of celluloid, compare those to what other manufacturers had to offer, back painted glass, sometimes back painted and etched glass, and mirrored too in the case of some high end Sparton models. The motor drive mechanism is about as crude as one can get, no presets, just a spring loaded switch.
 I think a lot of their appeal comes down to the fact that it's a name people recognize more since they were the last U.S owned TV manufacturer in the U.S, until they produced some sets with really crappy CRTs in the 90s, wrecked their reputation, and were ultimately bought out by LG. So I think that it's part nostalgia about the brand, and part reverse projection regarding the quality, from the late 1950s until the early 90s they built some of the best TVs out there, but whilst they were trying to beat out Philco and RCA in the radio business in the 1930s and 40s they were almost a cut rate brand that used flashy things like gold paint, big dials, bloated tube counts, and tone organs to sell their products. 
Regards
Arran