Even if she only "preaches to the converted" -- and I strongly disagree with you on that -- even that alone would "help the conservative cause" by providing us with tons of factual ammunition to use when *we* "preach to the unconverted".
Or are you going to try to tell me that you already knew every single bit of information and example and quote from all three of her books before you read them?
I completely agree with that. I think that the substance of what Ann does is incredibly useful in many cases. But she could accomplish the exact same thing without intentionally antagonizing people who might otherwise listen to her. You don't sway opinions by intentionally pissing off the people you are trying to convince.
As for the liberals out there, I could care less. They're not open to reason anyway. But there are an awful lot of people who may be open to reason if you can present them with your arguments in a reasonable manner. You don't have to be bland and boring to do that. Limbaugh toes that line well. He gets attention by saying things that tick off liberals. But the moderates chuckle, and consider the substance of what he says. That's how he's built such a huge audience, and even some libs admit they listen to him.
But Ann doesn't do that. She says things that piss off moderates, even when she could make the exact same substantive point in a manner that wouldn't piss them off. Regardless of whether you personally feel her methods are effective, the fact is that a lot of conservatives are not happy with her style. And if goes too far for some conservatives, how in the world can we expect her ideas to get through to moderates?