Amount of unsweetened chocolate in brownies recipe?
I think it would just be a less sweet/more intense chocolate flavour, based on how I've messed with chocolate levels in brownies before. If you enjoy dark, not tooo sweet chocolate desserts, then I'd say go for it. You could always frost them (ooooh, or top with caramel! or SALTED caramel!) if it's just too much chocolate/not enough sweet. Taste the batter before you bake it and you will know :)
It would be fine, and I'd even recommend it. The recipe I normally use is about half your recipe (recipes all seem to be either 13 x 9" pan, 1 cup flour, 1-1.5 sticks butter and 2 cups sugar; or 8 x 8" pan, 1/2 cup flour, 1/3-1/2 stick butter, and 1 cup sugar), and I use about 4 oz of chocolate.
The great thing about brownies is that it's hard to screw them up. A bit more or less butter, chocolate, sugar, or flour isn't going to ruin them. In fact, technique might be more important--for example, beating the eggs first will make the brownies cakier and prevent them from having that flaky, merengue-like top layer.
If I were doing your recipe and adding the extra unsweetened chocolate, I'd probably add a bit more sugar--maybe a spoonful or so, not to be too scientific.
I'd also add a little salt. Maybe 1/4 to 1/2 a teaspoon. Chocolate really benefits from a bit of salt.