Gravel and Sand were reduced to $0.00 during an update that killed Gravel Monsters. However, using a Gravel Monster had nothing to do with /sell-ing the gravel. You kept it and placed it over and over again. The point of doing it was for McMMO drops. Leave the McMMO drops OFF. But, there is no reason not to make these blocks 5 cents again.
Regardless of how you're able to dig these up, you still can't make more than $15k/hr. It's not going to be giving a lot of money to the economy, people would be better off using a normal money making method if that's what they really needed.
Its not about making money, just about what is right. Why dont we just make all 5 cent blocks be worth 0 if you cant make good money from them?
Your argument is a bit.. backwards. You're basically saying it's not necessary to give it a price because it won't make 15k an hour. With that line of thought a lot of things on the server would lose their value. It's a silly argument. Just because it won't make you mad profit doesn't mean it shouldn't have a price at all.
It's annoying to come across gravel while mining, or land clearing, and having to collect it, then get nothing for it. To stop people using gravel/sand monsters, yes, keep it out of the McMMO exp/bonuses stuff, and yes, let us be able to sell it and earn something for our effort at collecting it in the first place.