Diction (aka usage or “wrong-word”) issues are frequently cited as one of the top errors that the SAT Writing section tests, but the reality is that they only show up occasionally. In all the College Board tests I’ve ever looked at — and that’s quite a few — I’ve seen no more than a handful. It doesn’t matter if the other prep books include it all over the place; the College Board doesn’t.
So yes, while you should learn the difference between “affect” and “effect” so that you can use the words properly in your own writing, in terms of the SAT, I would not suggest that you spend your time memorizing long lists of commonly confused words. When usage errors do appear, they tend to be highly unexpected and often involve switching two words (e.g. “collaborate” and “corroborate”) that you’d never necessarily expect to be switched from looking at a “commonly switched words” list. You’ll either spot the error or you won’t. Besides reading a lot and developing a good ear for usage, there’s no real way to prepare.
At the risk of sounding like a broken record, my philosophy is that you should spend your time worrying about the things that are pretty much guaranteed to be on the test (subject- verb agreement, pronoun agreement, tense consistency, dangling modifiers, semicolons, etc.) and that are well within your control. As for the rest, it’s not worth your time to worry about. You can hit 750+ just focusing on the other, and once you’re in that range, it’s no longer about your scores.
P.S. In case you were wondering about the whole affect vs. effect thing, the former is a typically used as a verb and the latter as a noun: “I was strongly affected by the movie,” BUT “the movie had a strong effect on me.”