Consider this: For 105 points you have a squad in a droppod with 2 flamers and a combiflamer. I am contemplating a force with 3 droppods, 2 of which will contain assault squads with flamers and a techmarine with combimelta. The third pot wil contain a venerable dread with multimelta and heavy flamer. This combined with deathwing assault gives you the option of engaging up to 6 targets in turn 1. The deathwing will engage 2 targets due to splitfire, the assault squads wil each engage 2 targets due to the techmarines splitting of. First the techmarines open up transports with their melta's. Then the assault squads will flame the passengers.
Further options are giving the techmarines a servoharness, giving them a twin linked plasma shot, also for opening up transports, or use the flamer to add more hits to the hits generated by the assault squad.
Other things to consider are the face that the sergeant of the assault squad can exchange both hier bolt pistol and chainsword for a combiweapon, meaning that you can give him an combiflamer and combimelta, giving you more flexibility. Same goes for the techmarine, because since the FAQ he has bolt a bolter and bolt pistol.
I thing that assault squads are worth it, when used in the right list.