Well it has been a long time since I've heard "Joe's Garage"
but I doubt it'd hold up very well. That whole post-"Lather" era is arguably best represented on live albums like the YCDTA series so I'd definitely recommend checking them out. Though I basically lose interest around that period, he still released cool tunes. Even "The Man From Utopia", to choose a random lame Zappa album, has some cool instrumentals and a couple decent tunes like "Cocaine Decisions" and "Dangerous Kitchen". So for someone w/ such a large discography (and few of them are as large let alone larger), his stuff is pretty rewarding despite the inconsistencies in the later decades. And the wealth of archival releases, though predictably hit or miss, have yielded some incredible recordings which I consider essential for all fans.
"I don't know why he didn't throw his different styles together in one place more often, instead of doing a rock album, then a classical album, than a guitar solo album and so on."
Good point, and I think part of the reason so many fans (your truly included) tend to favor the early Mothers albums is because they're the closest to "Lather"'s type of eclecticism. Plus, there's the palpable joy of discovery and his compositions at that point were ####ing incredible, if not necessarily as complex as they would become