Oasis Problem
Right now, it is too easy to steal the oases without consequence. It makes the above mentioned cost hardly worth it. It does not matter if the defender is high level or low level, stealing is too easy. Again, leaving troops in the oases to defend it while the player is offline is not a viable option.
Let's face it: this is a war game and the World Map has PvP, but most people just cannot handle having "their stuff" getting stolen. It causes more anger and very little fun.
These NPC resource oases are a great game aspect in the advancement mechanism, but we need a better solution. Right now, I have one idea:
Have the oases not "droppable". Meaning, you cannot resign an oasis. The only way to lose an oasis is by Attack from another player, or when the system turns the oasis from level 1 to level 10 again. This will limit the number of attacks on oases for all the players and players will have to be very careful and selective of which oases they attack. No changes to Plunder. No changes to dispatching troops and heroes to your oases.
This is the same reason why not being able to resign castles and sub-cities works well. This would also help against people who steal oases for the sole purpose of harassment. These are people who don't use the oases and just "steal and dump" them all to harass people.
iOS 7.1.2 (11D257)
RotK beta version - current as of date of post