I think the Vistor idea is brilliant in its simplicity,
and makes raiding less dependent on a villager doing something stupid.
However I don't think that it solves the real issue with raiding, which is logging in one day and EVERYTHING being gone.
I think getting through defenses should be easier, however the damage that can be done when inside needs to be reduced.
An idea is that committing crimes adds 'mental weight' something like a curio to the study box, and when you commit enough crimes you have no more mental space to carry the weight of the crimes and cannot commit any more. The raider will then need to go away and 'reflect' or on the crimes before more can be committed.
This will give the raided group time to mount defenses for the next raid or decide to take what they can and flee the area. It will also mean that the raiders will not commit as much petty vandalism because it consumes mental weight, which could be better spend on the theft of valuables.
The mental weight can be calculated by the type of crime, higher for murder, negligible for trespass.
Then have something like charisma of the claim owner increase the mental weight. As charisma I assume is a reflection of someones standing in the community, so chieftains should be charismatic and this encourages the chieftain of a village to invest in charisma.
The amount of mental weight a criminal can carry could use the same system as the curiosities, so the intelligence not only limits the amount of crimes that can be committed, but crimes also come with the down side of not being able to study as many curios/less LP gain.
I think a system like this would make the back and forth between raiding more interesting and it will have to play out over a wider time frame.