As a matter of fact, a person who may have once embraced the so-called "liberal" philosophy and then studied the writings of America's Founders, of Adam Smith, of people like Dr. Russell Kirk and other great intellectual giants in our history of conservative thought, tend to be better informed and more able to defend the ideas of liberty than others of us.
We have showcase "conservative" talk show people who major in provocative talk, and they have served a worthwhile purpose in arousing public dialogue, but they should not mistake themselves for authentic scholars and sole defenders of the ideas that underlie our Constitution. When they do, they appear childish and shallow.
One guy I have a massive amount of respect for is David Horowitz who used to be a radical leftist. Still, I would never nominate him for SCOTUS and it has nothing to with legal qualifications, I've known bus drivers who would make great nominees.
Miers is more of a chance than any conservative convert because she was in a place at the time of her apparent conversion that could be explained by opportunism.