Kaiyo is mostly correct. Spirit power is usually gained through fighting and reaching anew level of power within yourself. However there are a few ways to do it differently, i myself use it defensively at times as i lack any Kidou skills i use my spirit power to combat the stuff (for examples see Rumble in the Bronx, in Rukongai).
As for the suggestion it shall be taken into consideration but you have to understand that the system in place is very early almost a BETA version and by no means refined or perfected.
EDIT: Leden who the hell is that awesome artist you have a weblink to?