You never read a good book without being the better for it.
What role does それだけ play in this sentence?
Does それ refer to the degree with with you read good books / the amount of books you read? So the literal translation would be, “if you read good books, you’ll certainly become wiser to the degree you read”?
Could I replace それだけ with それほど？
@ericaw
それだけ means “X is on par with Y”. The marginal increase in X is the same as that in Y. It’s a parallel correlation.
So, “the more quality books you read, the wiser you will certainly become” is the meaning.
それほど cannot be used in this sentence. それほど is usually followed by ない (negation) — e.g. 良書を読んでも、それほど賢くはなれない。 (Note: さほど sounds much better than それほど.)
Replacing それだけ with それほど〜ない makes the sentence totally opposite.
By the way, I don’t think the English translation is best fit for the Japanese sentence. It doesn’t talk about a “good” book.