Rebalancing redux so that you get more of it for having only 4 shields would be nice, but here's another idea for pushing up their power. Each needs affinity 9 or higher:

Enhanced Shield of Flames - Searing heat occasionally scars the one fighting you.

Enhanced Shield of Waves - Much longer lasting (for water breathing). Gives extra redux resistance to all elemental damage.

Enhanced Shield of Earth - Gives resistance to piercing attacks. (already has a nice redux bonus, doesn't need much more)

Enhanced Shield of Slime - Hard strikes produce gouts of grease onto foe. Gives total immunity to bashing/lashing/whatever.

Enhanced Shield of Wind - Even more immunity to kicking, grants flight.

Enhanced Shield of Ice - Gives resistance to slicing attacks and occasionally deflects blows with it's hardness.

Enhanced Shield of Lightning - Parries metal weapons occasionally.

My other idea was spells that are only available to people with a high affinity in an elemental. Each spell would attempt to make up for a weakness on element has - such as affinity 9 in ooze would give you an acid storm spell - like pillar of lightning, unshielded people are whacked. Though it wouldn't be nova/pillar, it'd be nasty.

>Rebalancing redux so that you get more of it for having only
>4 shields would be nice

It's not linear, you know. Each extra shield is less and less DR. You have by far most of it by 4 shields.

I think a 4 path invoker is still a little niche, but 5 path is more than viable.

I've always wanted to scale the spells you can receive as an invoker based on your affinity as opposed to the learning rates. This sort of ties into the other long-term invoker request from last year to add more para-elemental paths.