In my main city, I attack somewhat often, although my rewards are not so hot.
In my secondary city, I decided to take a different approach. I keep almost to myself, and am placed in neighborhoods with similar players. Meaning players who mostly contribute to their own GBs. Meaning I can snipe 1st place for a relatively low amount and make a pretty penny. In a few weeks, my meager 500 FP supply more than doubled (I'll have to check), and I was able to get in contact with an Arc Goods seller to finally get mine on that world.