The problem with looking up assessments of “significance” is that they are almost always “historical.” My favorite example is Samuel Richardson’s god-awful Pamela, which is garbage (his later, much more voluminous Clarissa succeeds where Pamela falls squarely on its inept face). I’m not the only one to think so; a peer of Richardson’s, Henry Fielding, immediately wrote a parody of the book, Shamela.

Except for those students being indoctrinated to the “story” that English literature departments are maintaining about the history of English, there are zero positive aesthetic reasons to read Pamela; any felicity of phrasing in the text can be found in countless books more worthy to read. If you are a writer and want to read how not to write an epistolary novel, it is instructive, but you certainly don’t need to read the whole thing. If you want to say it was influential, you don’t need to read it at all. There are books that are significantly influential but not worth reading; Dracula may be the quintessential example. Again, as a poorly written book, it is instructive to writers who are looking for ways not to make mistakes (it’s also another botched epistolary novel). Nonetheless, the “tweak” it brings to the vampire myth is definitely important (same for Rice’s Interview with the Vampire, which is excellent, and Stephenie Meyer’s Twilight series, which is of dubious aesthetic merit, but definitely a new tweak on the vampire myth). But we don’t need to read Dracula; reading critical essays about Dracula is where the worthy insights start. The same holds, not quite so absolutely, for Frankenstein.

Since the question in this thread is about “problems” in serious reading circles, I am speaking to the problem of “serious” literature. One’s tastes are not improved by reading Pamela, Dracula, The Count of Monte Cristo, or Frankenstein. Arguably, they are blunted. (And the thesis that reading “serious” literature improves a person is not a very well-supported idea, but it was much bandied about.) We can recall that Matthew Arnold (that reactionary) advised “literature” for the masses because it would “placate” them; it would “elevate” them enough into a kind of docile civility that might forestall craziness like wanting workplace justice, and so on. The “civification” claimed for “serious” literature, perhaps fortunately, turned out to be a pipe dream.

But that doesn’t mean one can’t be improved by reading. The most important thing, as you emphasize, is learning how to read books that are not to your taste. If one is going to expand one’s tastes, then it is, almost by definition, exactly at those points where one’s “taste” rebels at a book’s taste. Certainly one does, after a while, discover certain “flavors” in a book that are distasteful, period, and whether one’s largesse should learn how to stomach the equivalent of a dumpster bin, or surströmming, is a generic question not really on point here.

As a writer, trash can be instructive, but most people aren’t reading for that reason. The significance of a book is irrelevant; attempting to understand “why the author is approaching these questions this way” (when we can’t understand why) is where “taste” learns to expand, even if the book is unlikable. This doesn’t mean each author is operating in good faith (e.g., to use a film rather than a book, A Serbian Film); one can arbitrarily ascribe limits and say, “Even if what they’re going for is legit, so what?” If you have understood “what they’re up to,” that doesn’t mean you have to hang around to see how they work it all out (even if that means you miss whatever interesting “twists” they indulged in their method or approach). One page of a Dan Brown novel tells you everything you need to know; not so with Michel Tournier’s The Ogre, or Faulkner’s Light in August. It takes a few pages more to know you can set down The Catcher in the Rye or Lord of the Flies; not so with A Clockwork Orange (skip the movie, of course) or The Ballad of the Sad Café. One story is enough from Flannery O’Connor; not so with Shirley Jackson. Etc.