I agree with you - these sentences are indeed overly complicated. (This sort of thing can happen when authors start talking about each other.)
Let's break these sentences down one at a time. Here's the first one:
To say them, however, is perhaps to talk more about the mind behind the words than the ends to which they are addressed.
"[T]he mind behind" is the author. "[T]he words" is, I think, the words that the author wrote - the words in the novel itself (Do Androids Dream...).
"[T]he ends to which they are addressed" also refers to the novel. The word "they" in this clause refers to the words the author has written - the words in the novel - and the novel itself is the "end" (or goal) of the author stringing all the words together.
As I understand it, Zelazny is saying that the qualities of inventiveness, wit, and artistic integrity apply more to the author of a novel than they do to the novel itself.
For to say them in all good-intentioned honesty about a story results mainly in a heaping of abstractions.
"[T]hem" is the three qualities that Zelazny has identified (wit, inventiveness, artistic integrity). "[I]n all good-intentioned honesty" means that Zelazny actually means that the novel has these three qualities - he's saying this with "honesty".
The "result" of saying these things about a story is "a heaping of abstractions". This "heaping of abstractions" is implied to be not a good thing; the abstractions are the reason why the three qualities apply to the author, not the novel.
This second sentence is building on the first one. In the first sentence, Zelazny says that the three qualities apply more to the author than they do to the novel. To support this, the second sentence says that applying the three qualities to the novel itself results in abstractions (as opposed to specifics), which is why those three qualities should apply to the author instead.
Wow, that was painful. To make myself feel better, I'm going to critique this passage. Buckle up, this will get snarky.
In the second bolded sentence, why does Zelazny have to inform us that his praise of the novel (and/or the author) is done with "good-intentioned honesty"?
This entire clause is unnecessary and somewhat ridiculous. Does Zelazny think that his readers believe he is being insincere in his praise of the book? Why would his readers possibly think that? I have never seen an introduction to a book that was filled with insincere praise; what would be the point of such an introduction?
The first bolded sentence contains not just one, but two vague and confusing ways to refer to a novel - and actually tries to talk separately about the novel and the words in the novel. This distinction is, of course, nonsense; a novel doesn't exist apart from the words that make up that novel.
The main sentiment expressed across both bolded sentences is that the traits of inventiveness, wit, and artistic integrity apply more to the author than they do to the author's novel. This is trite and obvious. Of course those three qualities apply to the author and not the novel. A novel can contain inventiveness, but the novel itself isn't inventive – a novel doesn't invent things! A novel can demonstrate its author's artistic integrity, but the novel does not have artistic integrity, because the novel does not create art!
The second bolded sentence only exists to expand upon the trite and obvious conclusion of the first bolded sentence - as though we needed additional explanation of why a trite and obvious conclusion is, in fact, trite and obvious.
Now, let me be clear: Zelazny has made an infinite percent more money selling his writing than I have (I have made nothing, having never tried). I'm just some Stack Exchange rando, criticizing a published, well-regarded author. So this critique is worth exactly as much as you paid me for it (which was, again, nothing).
But, still. It's easy for me to see why OP was confused by this passage. Sometimes, elaborate language winds up saying not much at all.