Adam,
There is no free lunch. For one thing, as you add blades, you also add profile drag. You also add cost, because any one blade is about as hard to make as another, even if they are skinnier. So if your blade cost doesn't go down, but you have twice as many, you pay twice as much.
Large helicopters tend to have more blades, like the 53E. I suspect there is a tradeoff between disk area and solidity. If they made the disk area on a 53E such that the disk loading was like a Schweizer 300, you would need bigger aircraft carriers to land on. But, with the extra blades, you can turn more horsepower into thrust compared to if you had lesser blades.
Building blades with twist is about as hard as building them without, and keeping them true. It takes tooling and processes. So, once the tooling and processes are set up, building twisted blades is no big deal. And since we can track & balance them, that's not a big deal either.
I would also suspect there is a limit to how big you can grow a rotor, eventually the rotor would not be stiff enough to support itself when not turning. It would seem to me that getting the aeroelastics stable on a loooonger blade could be a challenge too.
I don't think it is just loads and high stress that killed wooden blades, though that is certaintly a factor. There was a high-profile FW accident before metal airliners where the wooden spar failed due to either dry rot or termites (if there are any historians out there maybe you can help me out on this statement). Metal doesn't dry rot (though it might corrode) and bugs don't eat it. And, good wood is harder to come by, it has gotten pretty expensive. If you ever build a wooden homebuilt, and have to buy spruce spars for the wing, you will pay a lot more than a comparable metal spar. The stuff may grow on trees, but slowly, and you won't be buying it at home depot.
-- IFMU