1. MB is one of the reasons why they added this system in the first place. A friend of mine had problems on their home server where food could cost 70k for piece NQ when it was 20k for HQ on mine. Or minion costs 2kk when it's 500k on mine. A lot of people tended to overprice their items on MB because they knew that buyers have no choice anyway so they can please their greed as much as they want. In long-time perspective cross-DC MB will balance this issue because sellers and buyers will know that they have options.
(fun tip: prices on EU servers MBs are 5-10x higher than prices on JP MBs normally. Can't say about NA)
2. Hunts need to be reworked as a system itself if we consider them as server content, especially 50 and 60 lvl since they are soloable if you are 70th lvl. It was addressed to the DevTeam few times. Still no changes for now, mainly because DevTeam do not consider it as "server content" in the first place. It never was a server content, technically (in contrast to Odin FATE, for example, whom you can't beat in solo even on 70th lvl).
3. As for community issues, well... don't really know what we can do here. Even with hunts - it was an issue there already long before Visit System. There are no any restrictions about killing them, they don't belong to some specific party. You found - you killed, you have full right for it. You can be a nice person and share info so other people will be able to kill it too, or you can kill it alone and while other players definitely will be angry about this (if they will find out at all that you killed the hunt, though), there is nothing what they can really do about this. Also there are parties of friends who running around and spawning S-ranks and it's really up to them to decide if they want share info about or not independently on being at Home/Visited server. Hunts are called "Hunts" not for nothing. You need find them by yourself. Killing hunts without waiting is not against rules because actually it is how they were designed to be. The whole thing about Hunt Linkshells and organized "rules" about it was a community initiative, not part of their original design.