This will be wars between guilds
There should be a servar were guilds can fight openly (since gw2 will be one big world unlike the lobby system we have now) and take over towns from each other (imagine how wild it would get) After a town has being captured you can loot it (il come to that later) and get people to work for you. Guild halls would be like towns but they can not change hands.
To get people to work for you money would have to be invested at the start of the week on which towns people will work for you geting matrails that can be sold to make a profit depending on how much you invest. You can build new buildings (towers walls houses (to make workers work better) etc
To do the above you would set your guild to Conquest guild
To do the bellow you would ser you Guild To Raid guild
As a raid guild you could attack guilds without declareing war (which costs cash) which lets you attack anybody not in your guild raid guilds can controal towns but not invest so the source of income would be from loot but workers can be turned into slaves.
Slaves dont work so well and can only build and do primary industries (mineing fishing etc) and will run away if ungaurded.
Raid guilds are ment to attack Loot and escape slaves may be useful if makeing a tower or something is needed to hold off a attack
Oh i know this would not work in GW1 so this is a GW2 iddea feel free to add