BB_RobinHood3 was running around on the Sandycove server earlier looking for feedback about PvP and suggestions for it.
From what I can gather from both myself and my Guild, these are the problems that detract from people doing PvP:
Troops are slow to make, even with the academy at 6.
Weapons are the most painful part of PvP. The time it takes, buffed, to produce any weapons, at 6, is again, painfully slow.
The costs are high vs the reward.
The combat system is puerile.
The colonies are too simple to conquer. You conquer it, 12 hours later and it is gone. A waste of troops and resources. Levelling system does not help in this manner at all as all that happens when you level is that you get a few more rewards and those rewards are not worth much.
Maintaining 3 separate armies is annoying.