Any seers feel free to correct me on this, but as I understand it control of the stones is very handy on the combat
front. There are various skills a Seer can use through a stone, such as bonding, curses, immolating an area, watching, traversing... These can also be used through a portable stone. The limitation of course, is that you can only do these things throug
h an area you control.
So assuming for the minute all three seer guilds want the treaty, and the rest of us abide by it, there's plenty of reasons for the seer guilds to continue to fight over stone locations, for their own guilds' benefit.
The biggest flaw I see is that if someone breaks the treaty, or is perceived to have broken it, then the wronged party
will have a nice big reason to go back to shop robbing, and the rest of us will have helpfully provided big fat shopsfull of goods...
Written by my hand on the 2nd of Agamnion, in the year 1076.