Saska is right here. If you want to grow fast than you need the resources. Think all the way back to when you first started.... The higher your resources the faster you could use them. Then think to when you had 5 or 6 cities and all of your resources are maxed and you have the academy and senate maxed you can run city festivals once or twice a day and the more cities you have the more festivals you can run. This will have a constant flow of CP without losing your Soldiers. I play gamma and have over 100 cities think about it if my recourses are maxed I can run 100+ city fest twice a day, Yes I could gain CP from BP, but not at a constant rate because you have to rebuild and then miss a few days of attacking. To do it the way that Saska has said you not only get the CP at constant rate, but you also can use your soldiers to fight real battles rather than waste them just trying to get CP. In the end it is better to max the resouces and have constant flow than for me to waste the soldiers I could use to save or take a city.
One more thing by getting CP from bp you leave yourself vulnerable because you are constantly rebuilding. I was very good at taking a city from a player who would waste their soldiers attacking me for the BP. Oakenwald can attest to this.
Quay