Indeed, Wildlands are a bit disappointing at times. Especially because I love the idea behind them.
There are some additional ones in the map pack (I think) that have a wider span of difficulty. The darkling city for example. It is realitively easy to take and provides an interesting bonus, long before the game is decided.
I would love to see more of that and a more diverse set of rewards for clearing them.
Ever respawning Monsters would be a nice thing as well, but it would be incredible hard to balance. A constant stream of XP for the armies in the area is a bonus in itself.
So, what could be done about it?
So, for the realistic part:
Provide alternative means of conquering the wildlands.
Add three to four nodes in the wildlands. All guarded by a stationary monster army, far less powerful than the main guardian. Clear all the nodes, clear the wildland.
Add a shrine to every wildland. Go there, sacrifice a hefty amount of ressources, clear the wildland.
Have a number of outposts at the border of the wildland and build a dedicated wildland domination building in all of them (has to be added), clear the wildland.
What happens to the guardian?
Either make it stationary or have it disappear alltogether. I'm not really in the mood to talk about that though
Read more on something that is far less likely to happen
Unrealistic "that would be so awesome option":
Capture and hold type:
Generally small wildlands with a structure in the center, providing a significant bonus similar to the current ressources, just on steroids. I'm thinking of a +4 shard, +3 Material or +15 Gildar thingy.
The mechanic behind those would be, that an army has to be positioned on the ressource to hold it. As long as this condition is met, the bonus of the ressource is provided to the nearest town or the empire at whole. As long as the ressource is occupied, monster armies spawn on a semi regular basis and try to liberate the ressource. Those armies don't provide heavily reduced XP and never leave the wildland.
Generally medium to large maze like wildlands, filled with loot and higly active, but clearable monster spawners. Boss type creature at the end or center providing an item, ressources, a hero or a combination of these when slain.
Generally small areas that have respawnable monster spawners which in turn spawn monsters that roam the general area around the wildland, rading and attacking what they find. Clearable... for a while (Until the spawners respawn)
These make the area around them a dangerous place to dwell.
Optional: A ressource intensive way to clear them, possibly unlocked by a tech.
Armies to keep them at bay, while you gather the ressources to seal them.
Current type, but with changed rewards. One ot two city spots with a "Holy mother mary of god" quality.
Most of these would need drastic changes or additions to the AI, as well as a lot of work, so it is rather unlikely to come anywhere outside its own expansion.