It's easy to ignore int for characters that use only single target instant damage effects. Also, extended duration only matters if the effect runs its course. In combat, it's almost always better to focus down individual enemies quickly as opposed to doing steady damage to all enemies at once.
As a question what mode are you playing on. Hard and PotD fights tend to be more than long enough to justify 2x duration effects. In a game with limited resources per combat like this one, crowd control and dpc(damage per cast) are far more important than single target damage. I can not think of a single class that doesn't benefit from intel in an appreciable way. Not even rogue as 25 second hobble = 25 secs of 1.5x damage via sneak attack trait.
