I still don't think I've listened to Slanted enough to compare it yet, but even so, I agree with your Godfather analogy. Also, in terms of Crooked possibly being fully realized — it's often the case with first records, but I think Pavement may be one of the few exceptions. The rawness and youthful exuberance and unpredictability is what makes them an amazing band. There's no reason to desire less of those qualities — granted, they maintained them through Crooked and Wowee, but Terror Twilight sounds a lot more like a professional band deliberately setting out to record and polish defined pop songs with defined song structures. I still like it, but a lot of their core is lost by that point. I don't think they really sacrificed anything, personally, to make slightly more polished — not going to say realized — music on Crooked, which is why it still stands for me. It might represent some small level of maturation at the expense of some rawness and lo-fi grungy sounds, but the songwriting is as raw and fresh as ever.
Still, other really quirky bands like Modest Mouse and especially Dismemberment Plan, who probably owe everything to Pavement, obviously were heavily influenced by Slanted. The only pre-cursor to Slanted might be Pixies, right? I can't think of anything else.
I agree with your sentiments toward Terror Twilight. In fact, the band does as well. They are unabashed about expressing their regret when it comes to how "produced" that album sounds. On paper, Pavement + Nigel Godrich production seems incredible, but it took away what was special about Pavement — the beauty of the unpolished. Then again, I actually have no problems with Terror. It's a fun album, and it's cool to hear Pavement through the ears of Mr. Radiohead. As you said, Crooked is somewhere in between Slanted and Terror, though I'm sure you'd agree it leans more to the Slanted side of the spectrum.
I'd be hard-pressed to believe that Modest Mouse hasn't listened to a lot of Pavement, but you never know. Isaac Brock is notoriously hard-headed and might not admit to anything. Travis Morrison from Dismemberment Plan, on the contrary, would be happy to reveal his influences. I say this because he once ran off the stage and made a bee-line to hug my friend Farbod because he was seemingly the only one enjoying the show. They stayed in touch and actually held a BBQ where Morrison played a solo set.
In regards to your "Pixies lacking a pre-cursor" statement, I can't argue. Research tells us they had already released three albums (including the acclaimed Surfer Rosa and Doolittle) by the time Slanted was released. Then again, I like Pavement much more than I like the Pixies. In fact, I remember when John Stirratt's cousin (Wilco) quoted me in his Facebook favorite quotes for writing "Nobody actually likes the Pixies. They just think everyone else does." I was exaggerating for effect, but it felt pretty good as a budding music journalist. A few days later he removed the quote, probably because it appeared lame to quote a kid writing in the school newspaper.