The people his comics appealed to didn't need convincing because they already believed and to people on the fence they looked ridiculous.
I question that. There's a lady at our church that leaves Chick tracts in the lobby, and in the pews. She was, at the very least, a fence-sitter at one time, and possibly involved in some of the things Chick would call witchcraft. I don't know if she, herself, came to the faith through his ministry, though.
I keep an eye out for her tracts, and take them home and throw them away, as I also fear they're more hindrance than help, even if they do help people, occasionally. I usually read them before I toss them. His anti-Catholic tracts, or the ones I've read, had a lot more citations of Catholic authorities than I would have expected (several, instead of zero).
I'm skeptical of Bible tracts, and not just Chick's, as I find it hard to imagine anyone being influenced in any deep way by what is essentially junk mail. That being said, tracts have worked for people, so I might be wrong. I wouldn't want to be so intolerant as to think someone else might see them differently than I do.