I share your sentiments about Insomnium, if they would just drop the growling and use clean singing all the time (like they have proven they are capable of with in a few songs which are sung by I believe the same vocalist who does the growling so that means they wouldn't even need a line up change) I think they could really make the big time.
I actually don't like growling in the music, I just love the instrumental sections of the music so much I deal with it. I'm considering learning to sing and dubbing over my instrumental covers of theirs (I've got some Insomnium ones recorded too btw Ric, I just have to upload them) with normal singing, maybe showing what "could have been".