Many thanks Gentlemen.
Both answers seem to confirm my intuition, even though they're slightly at odds. But in the main, we'll defer to Mr. caster.
Yeah, in general, I don't find 1960 cabs unreasonably priced (350-400 used when they come through the local GC), but I'm not wild about the stock G12t-75s. So it was always: "If I'm likely to swap out the speakers anyway..." and that inclined me towards something offbrand and lower-priced.
It's hard to get a straight answer sometimes on particular downmarket cabs. Google, obviously no help, and you find yourself wading through boards full of people saying that a cab "rhulz" or "sucks balls!" And you're like, "yeah but what if you got rid of the OEM speakers which seem to be the least impressive Celestions that bear the name." One goes down these rabbit-holes far enough, and you find two guys debating pine versus birch with all the fervor of the Protestant Reformation.
But it does make you wonder how much these things matter and what truly does.
Champagne problems (my Fender Prosonic is admittedly plenty loud already; a 4x12 is arguably self-indulgent), but I'm glad for your insights. Everyone on this board has always struck me as reasonable and civil, a delightful contrast to the internet in general.