OK, just a quick note, this conversation shouldn't be about how worthwhile first edition spells are, or whether it's worthwhile to be a spellcaster.
Also, this isn't necessarily about how effective magic is, but about the wider issue of how it functions in the game, so let's stay focused on that.
Your analysis is excellent Philaros, however there are a few things to clarify. On saving throws, they apply in exactly the same situations in ApocD&D as they do in AD&D, which is when the spell descriptions say they apply. The effectiveness of ApocD&D saving throws is not the same as AD&D saving throws, however, and they don't scale by level in the same way.
That said, saving throws work very, very differently in the two games, and that's a function of the basic difference between them. Only PCs get saving throws. No monster ever gets a saving throw.
Also, note carefully that a miscast never automatically happens. It's not a penalty for a failed roll, any more than any DM move in Apocalypse World is a penalty. You're starting to think in terms of "if I try to cast a spell, I may fail!" That's D&D think. What you should be thinking is "if I roll the dice, the DM may get to make a move." Think of the miscast table in those terms. Roll on a random table is one of the DM moves. The miscast table just provides a specific instantiation of this move.
I'm also formulating some more specific thoughts around Phil's posts, but I really need to digest them more, because he's pointed out some really good realities there.