My thoughts on the Soul Gems was more for the Greater Bane than the Lesser and regular banes. Although what you suggest does seem to make sense. I pointed out that there were no soul gems for dragons, but others have pointed out the gems in rare chests needed to flag for SoS covers that. I think that still leaves one creature type that would be a sticking point for the weak, regular and strong soul gems: constructs. I might be wrong, but the only constructs that can be turned into soul gems are Fleshgolems, but I've only seen Weak Living Construct Soul Gems. I'm sure someone will correct me if I'm wrong about this though.
I have no casters. I have a bunch of Soul Gems though. It's because I have an Epic Souleater. Others have pointed to GS Vacuum weapons as another way for non-casters. Maybe I'm in the minority, but I have so many Soul Gems, I don't know what to do with them. What would I do if they became a crafting ingredient? Probably give alot of them away. (Yeah, others would try to make a buck off of Soul Gems, just like you'll see in the AH now with outrageous prices for the completely useless ones. Just as people try to sell Bloodstones for "the" Bloodstone or old Ioun Stones for suppressed Ioun Stones. Heck, the DDOStore sells small ingredients that most people give (not trade) to others without pausing to think about it.) Sure, the Souleater doesn't go off consistently so that its unreliable it to get the Soul Gems you want when you want them. But it goes off enough that you will have eventually get the Soul Gem you want (and more) that if it's one Soul Gem per shard that giving them away wouldn't be unusual.
However, if it's like the Adamantine ritual, I can see your point a bit more. Getting 10 Earth Soul Gems can take some time with an Epic Souleater. The 150 Soul Gems for the maximum Adamantine Ritual is too time consuming for a non-caster.