It's very easy to say "we shouldn't critique classical novels" and I understand that this is seen as sort of the "correct" position, and I understand that it stirs up a lot of emotions, for whatever reason as well. Let me, however, try to make three points as to why either this, or something like this is useful.
1) It can help instruct some people as to whether they're using their time/energy well or not.
Let me give you an example from physics, since that's what's most familiar to me.
Einstein's 1905 paper on special relativity was brilliant and it changed the world. Literally all of modern physics has it as part of its foundation. However, would that paper have been published today if we applied modern standards for scientific articles? Absolutely not. There are several red flags that would have prevented it from even being sent out for review (as an aside, I'm not even sure if Einstein's paper on relativity was even "reviewed" in the modern sense. My guess is that it wasn't). For example, he doesn't cite a single reference, which wouldn't be allowed today.
So, lets say you want to learn how to write a scientific paper. You could say, "I'll start with the greats like Einstein", and you would learn almost everything wrong by the standards that it would take to get published today. That does not mean there's no value to reading his paper.
Similarly, lets say you want to write a great novel, and you say, "I'll start with the greats, like Hemingway or Fitzgerald." I know many people here, probably know better, but a good question to ask is how much are you learning "wrong" by today's standards, assuming you want to get published. That doesn't mean there's no value to reading Hemingway or Fitzgerald.
2. It is still worth asking if great authors did something wrong.
Let me go back to the Einstein example. His paper on GENERAL relativity is ALSO brilliant. General relativity is the second best tested theory of all time, and everything we've seen confirms its predictions. However, we also know that it MUST be wrong on some level, because it can't be quantized (owever, the point where it breaks down is at much higher energies than what we can observe). Additionally, Einstein said a lot of outright stupid things (knowing what we know today) about quantum mechanics.
So similarly, there are likely legitimate flaws (although I realize this is subjective) even in great works of literature.
3. It tells us something about ourselves.
When I first read two of the three books I posted excerpts from, I really enjoyed them and thought they were really well written. Looking back on them now, I think "man, this sounds kind of awkward." So, have I become too absorbed in my own writing style to appreciate others? Have I become too absorbed in modern literature to appreciate the greats of the past? It's worth thinking about.
Critiques above complained about the unfamiliar use/meaning of the word "powdered", or the need to tell which direction a room faced, or the complex structure of a sentence with several "and"s... This doesn't help expand horizons and learn new things.
Anybody can have an opinion as a reader, or even as an unsure guesser. But that doesn't help learning. Learning is taking something that's established to be good and attempting to see why it's considered good (or even "great"). One person's personal dislike doesn't help, especially when there are many, many more who found something great in that work. One person saying they don't like Hemingway doesn't help an aspiring writer learn what was so great about Hemingway. The better question would be to ask why Hemingway's writing is considered so good. 
