According to court papers, the suit accuses the defendants of breaking the law by limiting radio airtime for musicians who used competing concert promoters and inflating musicians' fees, "in some cases more than 100 percent of gross sales, in order to exclude competitors from the market."The AP adds thats the suit also alleges that Clear Channel denied advertising opportunities from other concert promoters and/or charged extremely high prices for poor ad slots. Clear Channel's former promotional subsidiary, Live Nation, is also named in the suit.
Personally, I don't think this could have had much of an effect on concert prices (even if CCC engaged in anti-competitive practices) because concerts from different bands are not really very good substitutes for each other, and competition among concerts from different bands therefore doesn't seem like a good reason for ticket prices to have been so low. (That is, when there is excess demand for your tickets, you don't face any effective competition anyway, so this can't really explain recent trends.)