My thought would be that they'd want something more disruptive to the stability of our way of life.
Taking out a nuclear plant or two would definately de-stabalize our energy system and drive the cost of oil up.
You seem to see the key angle of this campaign - the high body counts are frosting on the cake, which is an assault on the US economic infrastructure, which is the main things these nuts really hate about us. Transportation systems, mail systems, power grids, computer networks - these are the likely targets of the evil ones.