I think people's desire to make the chaos star mean more is more an issue of lazy GMing than the rules. They want a straight rule effect to give them punch when really they should be adding more serious complications to what is happening in-story. The Player's Guide has a short section on this that gives a good starting point on what is appropriate.
Adding challenge symbols rather than harsh "bad critical" effects makes the story less interesting. It's more interesting to have a character hit, but then lose his weapon or get slammed in the face and go blind for two rounds, than just "miss," which is all challenge symbols do.
If players don't fear chaos stars, it's not because they are underpowered. It's because the GM isn't doing his job in making bad effects and setbacks .