Kill two birds with one stone: increasing traffic to the world, and lining your pocket.
Make claims something which, in some manner or another, can be perpetuated with money. Probably with a lot of caps and restrictions.
One of the really tiring things about this game is that you need to keep finding and making curios to hold onto your plot of land. After about a month of coming back and playing, I've had my fill. But I can't quite stop because I have the bad feeling my claim will die out and I'll lose all my neat shit.
Now I'm a hermit, and I have a lot of crappy stuff nobody wants. I don't have much to protect or worth protecting. But if I had a plot of land the size, say, about the size of 2 great halls, where I could build whatever I want and guarantee its safety, so long as I pay $5 or $10 a month, I would do it. I would be more likely to come back because I wouldn't have to build from the ground up because of looters. If I wanted to move, and move my 30x30 plot, I should be able to provided I give up the land it currently occupies. It should be adjustable so it never takes up more than 900 squares of land total, but no narrower than a log cabin and its border tiles.
Another restriction is that the paid-for claim should not be allowed any closer than 60 tiles from another paid claim, and perhaps users should be limited to 2 for $10-20 - or 3 for $15-30 a month - so that griefers cannot make an impenetrable "great wall" to block out players from areas, and "whales" cannot buy half of the world (y'know, unless unbridled capitalism makes the game more fun). Since one could use this to preserve landmarks such as markets or Great Hall sites as well, it should be able to exist within a village - probably it should not be buildable in a village unless you are a hirdsman or lawspeaker. Lawspeakers should not be able to revoke this claim, since he has not paid for this lot to exist; therefore ordinary villagers should be forbidden from building bought claims in a village.
They should also not be permitted on resources; only on land, sea, or the underground away from fairy stones, clay pits, etc.
Just having land I can be sure I can come back to in a few months, or even half a year or a year from now, would make this game much less stressful, addictive, and difficult. It wouldn't become an addiction in the worst way, because eventually it all becomes about fear of losing your stuff. Offer to remove the worst of that fear for a small fee, and it's a win-win.