Allow governors to set tax rates and mode of expected payment (cap it so it's not something ungodly) to people in their city region. I can't see any governor with half a brain cell abusing that to members of neutral or allied guilds (if they applied one at all) who are actual productive members since more foot traffic and trade is good for everyone.
Allow for a status to be declared towards another guild like allied, friendly, trade partner, and war. Allow any member of a guild at war with the guild controlling the city to be PvP hot in the city. If they want to leech, make them earn every drop of blood.
This not only fixes enemy guilds from abusing other guilds who actually took the time to install logistics and maintenance plans, but it also STRONGLY encourages guild diplomacy and politics.....which leads to HEATED wars. It also places just as much value on the player leaning more towards PvE and trade as it does the player who likes to wtfown people and build an empire.
More importantly.....it avoids a MAJOR avenue for griefing. Because a small handful of players can use this open city/territory system as a way to put all trade and lvl'ing in that area to a grinding halt doing basic hit and runs from the safety of their housing. I assure anyone who thinks this is a good idea....under this system I could make you rage quit inside a week tops.