For now, you don't get any reward by defeating an invasion, without considering alignment points or loot gained by killing its troops of course.
So, I have an idea that will make fighting invasions a bit more rewarding.
After all the waves of enemies are defeated, the hovering sword (that one hovering above ground, marking the invasion point) falls to the ground like a spear does. Then any player that hits the sword at least once in 10 seconds (the bosses have a similar system to grant its achievement to several players), will get an alignment reward (if it's a Gundabad invasion, you'll get alignment points with factions that you normally gain alignment by killing Gundabad orcs) and then once the timer runs out, the sword explodes, dropping coins, ingots, food, memes, flamethrowers or anything that the mod team considers a balanced reward, in a radius of the explosion, marking the end of the invasion.
The quantity of the reward depends on the number of players. If 10 players hit the fallen sword, more loot will spawn than if only 5 players had hit it. But the reward shouldn't scale directly, like 40 coins per player, nope, let me explain:
Example (these values are for the purpose of this example alone): 10 players get 10000 coins, while 5 players get 8000. Surely the 10 players got more loot, but each of them will only get a share of 1000 coins, while each of the 5 players will get 1600 coins. I'm sure that Mevans & Co. will be able to transform this into a math curve or something.
Now, it may happen that a greed player collects more loot that the others (that's why the loot should drop in a radius of the sword), but that's the problem of that player group and they should decide how they're going to share it. If things get violent, well...
How it works:
Late additions:
> Things could be handled in a different way: Once the invasion is defeated, the hovering sword falls to the ground and several chests spawn, with loot and an item called "Battle Trophy", an item that you can exchange for alignment points with a commander, or any other kind that sells troops. Also, commanders could send you in quests to acquire Battle Trophies, and the reward could vary from coins, troops or even the commander itself! There could be Orcish, Elvish, Dwarvish and (Evil and Good) Mannish Battle Trophies, to avoid the player defeating an Haradrim invasion and then selling the Battle Trophy to a Mordor Commander, that wouldn't make much sense.