That's not a bad idea - an 18x18 area at one time? How much power do you find it generally uses for the dig? And how do you prefer to power that in the field?
I'm sure a Quarry would be comparable but it's such a pain dealing with all the dirt and cobble it digs up. I've gotten to the point where I usually use a Filler afterwards and put it all back.
The nice thing about Miners is, it's a neat little hole that is basically self-sealing.
I agree that the Quarry seems like a massive waste for what it picks up. I'm intrigued by the idea of setting a filler up to replace all the trash it digs up, but there's also the potential of turning its output into scrap for a mass fab. Isn't that the engame of IC now?
I currently consider quarries as something to build to use up oil deposits and gather me some building materials, however all but the most massive builds are going to be easily satisfied by a quarry's output. When it comes to diamonds, a miner is my immediate choice. An OV miner should be almost guaranteed to pick up a diamond vein. If it doesn't, then replacing it 10 blocks over will definitely get some. Right?