For "protecting the nevernever", I had a concept for a whole other world once that might work here.
The idea was this: There are "wanderers", ordinary humans who constantly feel the need to travel. What they and most others don't know is that they are linked to the magic of the world, the way they are drawn is such that it shifts the magic around on the planet, so that it is distributed best.
There could be similar people for the nevernever. They are linked to the walls but not consciously, they are simply drawn to where the walls are weak or leaking and they stay there until their presence fixes things.
But sometimes a wanderer might become aware, because the problem is so dire that it needs conscious actions to repair it.
When it comes to Gaia, you're eventually going to run into the Sidhe, because that's pretty much the niche they fill. Then again, Gaia might still be around, she's just lost a lot of her power and is now a genius loci that the character stumbled upon. She can't leave her land, but she can bestow some of her power onto an emissary.
I would say that such magic would encompass a mixture of seelie and unseelie magic, since I would say that's where it comes from in the first place. However, you wouldn't just have both, you'd need to go with the flow of nature. Not only the seasons, but also the problem at hand. You can't solve a problem of overgrowth with Summer and you can't solve a problem of stagnation with winter. So solving a problem of stagnation would be a lot easier in summer, for example.