FFF has always been a personal favorite of mine, so happy to see it get its due as well. I wonder if the awkward title plays a role in it being underrated as well.
Journey is a mixed bag for sure, but I enjoy the first half of it well enough (at least until Race Babbling). It's not mindblowing or anything, but it does create a certain mood in my mind of a rainy, humid morning, so if using Brian Eno as a comparison, the ambience works for me. The stretch from Outside My Window through Ecclesiastes is nice too. But it's too long of course, and I've always found the last four tracks to be simultaneously bombastic and boring.
I have some fondness for the pop era of Stevie Wonder, or at least I think his sense of melody never entirely deserted him. But yeah, the shift on Hotter than July to a more commercially-oriented production style was certainly a harbinger that he was never going to return to his peak. I kind of enjoy the more up-tempo songs on The Woman in Red (I admit Don't Drive Drunk is objectively bad, but I still find it goofily entertaining), but the ballads are pretty awful.
I'm curious to see what you think of In Square Circle and subsequent albums. I have a feeling you'll rate them a lot lower than I do though. Though really, In Square Circle and Conversation Peace are the only remaining Stevie albums that are even in the 11/15 range for me. But overall, I think Stevie still had a less embarrassing 80s than a lot of others, maybe by virtue of not releasing all that many albums.