Re: "it's as close as they ever got to making a straightforward 'serious' rock album."
I dunno- in some ways, "Quebec" seems "browner" than "White Pepper" to me. As you mentioned, there's pitch shifted vox and none of that on WP and there's also the opening cut which is a pretty obvious Motorhead pastiche (also my favorite cut despite not being a Motorhead fan at all). It just seems "brown" in a pretty uncreative way- yeah stuff like "So Many People In The Neighborhood" is weird but also arguably pretty dull, like a failed attempt to capture the magic of their early albums.
Also notable that "Ice Castles" was always my favorite WP track- the album's brownest moment by far, genuinely weird yet beautiful rather than just a dull retread of the early stuff (though "Stay Forever" is way up there too- another beautiful tune).