The alternative is for the PTO to close prosecution and issue an invalid patent.

I am not sure that this is even an option really. The rule is supposed to be that once the PTO loses in front of the CAFC, they are supposed to issue the patent, not reopen prosecution. In re Van Os, 844 F.3d 1359, 1362 (Fed. Cir. 2017) (Newman, J., concurring). Sadly, this is recently become a rule more honored in the breach than the observance.

[W]hat a waste of client money to have to go through a second round of examination arguing obviousness on remand back at the PTO in order to further develop the record… A better and less expensive practice is to properly develop the record on all rel[eva]nt grounds before the Examiner the first time.

Sure, no argument there. Much better to put the right rejections on the record, rather than the wrong ones, so that the case might be correctly decided. In a world run by humans rather than angels, however, some number of mistakes (even expensive mistakes) are simply inevitable.

At one time, Examiners could (and sometimes would) reject claims under 35 USC 102 and 103 in the alternative; but this seems to be very rare or no longer the case…

Really, is this rare in your experience? Quite the opposite in mine. I would say that—of the office actions that I see that include an anticipation rejection—there are more that also include an explicit obviousness rejection in the alternative than office actions that only make the anticipation rejection. In other words, in my experience (mostly art units in the 1600s), examiners usually make the 102/103 rejections in the alternative. As you say, this seems to me a good practice for compact prosecution.