I can totally see where you are coming from, however I never grade homework.
It takes us maybe 5-10 minutes to go over a homework assignment the following day and it should only take them about 10 minutes to complete it at home. Of course, I also ask that they read something for 15 minutes nightly, just to keep them reading. I don't assign them anything in particular to read though. I do feel that even if students have mastered content, that it doesn't hurt them to have a refresher every now and then. I know in my classroom, I don't teach something once, check for mastery, and then never mention it again. For example, when I teach a shared reading lesson, we'll review author, illustrator, text features, etc. on a daily basis. We may be talking about cause and effect that week, but we will still identify contractions as we read, or any number of other skills. It doesn't take a long time to revisit previously taught skills and I feel it's always good to keep reminding them with a quick refresher using gestures. I can tie many skills into my shared reading lesson or any other lesson I am teaching.
Back to homework though, I never give them something that hasn't been taught and I don't feel they have a firm grasp on because I don't want them to learn it wrong. Research has proven that it takes more time to unlearn something that was learned incorrectly than it takes to learn it correctly the first time. It also doesn't take me long at all to check to see if homework is finished, because I have student leaders that will take my clipboard and check to see if it is complete and mark the students' homework calendars. My kids look forward to having their homework checked and answering the questions when we go over it. Plus, it's a great motivator for the scoreboard as well. If they beat me in the scoreboard, I can always say, "Tonight you only have to do the odd numbered problems." They love that!
I hope this helps some.