Hell it seems like the Genius Bar has always been packed, I remember having to go in the morning before opening for my Power Mac in 2003 and waiting around with a few others for repairs. And besides being the place to go for problems, there's only so many of them around, and afaik they're generally placed in high traffic areas.
As far as hardware quality in general though, if anything I'd say it's better, but I don't really have an objective basis for that. I'm talking a long term view too though, like before x86, everything is a lot tighter now.
That said I still generally follow the avoid rev. A thing, but it's always been a loose rule personally. It could be for a new design where everything changes, where I think they've gotten a lot better and fixed stuff faster nowadays, or just for new internal hardware, which is where the looseness plays in. A "rev. B" could be nearly identical externally and still be completely new internally. These days I feel like I wait for revisions more for wanting particular features (like TB3 currently) rather than being worried about issues with first gen hardware.
I'll have no problem getting the next Mac mini immediately if it's a full on redesign that has what I want (...not that I actually expect that).
(And for a general industry wide footnote, look up lead free solder problems)
