Probably would have come off kitschy instead. (A contemporary case-in-point comparison point: the Normal School facade in the Ryerson campus--though at least they subsequently made nicely PoMo use of it as a underground-gym-facility entry.)
And back to...
Except that unlike freshcutgrass or US, I'm stopping short of playing a retroactive "endorsement" game. Rather, I'm treating that 1964 moment as "historical" in its own right, i.e. as removed from the present as if it were 1864 or 1764, and explaining why it's folly to overimpose our present-day values in trying to "comprehend" the increasingly un-recent past. But also, by extension, why it's folly to over-lionize said increasingly un-recent past. I mean: sure, there are those Rem Koolhaas types who'd apparently like to return to the days when Great Architects could boldly sacrifice an humdrum old crock like the Registry Office; but realistically, they're working against pro-old-crock arguments that have gone from the "pretty buildings" alibi of the 60s/70s to more comprehensive social or green/embodied-energy concerns.
Though I can also comprehend the fears of pro-moderns like Koolhaas; that is, the urge to over-lament the Registry Office loss as if it were yesterday can easily collapse or feed into a hyperactive "revenge desecration" urge, particularly among hyperactive anti-moderns and overzealous New Urbanist types. (Sort of like the problem faced by the Boston Government Center, City Hall and all, i.e. the perceived aesthetic sins of all that Brutalism are magnified once the anti's conveniently whip out the old photos of Scollay Square: "see? this is what it replaced", bla bla bla.)