Currently a P-Claim naturally progresses to a V-claim.
This suggestion takes the P-claim and gives it a bit more depth.
P-Claims now have levels (starting at 1 and maxing out at 5)
They also have a "days active" counter that increases by 1 for every day the claim has silver in it, and decreases by 1 for every day it doesn't.
Every 31 days active a claim can be upgraded.
Upgrade costs Claimsize x 2 silver
Each level makes it harder to increase claim size (new claim expansion formula is (claimlevel+4) per tile)
If the counter of active days ever reaches 0 the claim downgrades 1 level
Each upgrade allows "claim traits" to be picked
Some example traits are listed below (these are just examples and are probably horribly unbalanced)
Excellent Soil : All fields gain 10% plenty per planting
Festive Air : All foods heal 1.5x as much (3+ only)
Forest : Trees grow twice as fast
Fortress : Stone and Plank walls are 5% harder to break, rail fence and temp walls are 4x harder to break (4+, min claim size 100x100)
Hideout : Claim does not effect map (4+ only)
Lumbermill : 10% bonus to lumberjacking (10% more boards from sawbuck, 5% less rotten ones from piles)
Permanence : Increases cost for V-claim removal to 10x claim size (5 only)
Trained Defenders : 10% damage bonus to claim owner and those in his/her party when on claim (3+)
Wandering Camp : Can move claimstone once per 14 days at no cost (5 only, max claim size 25x25)
Optional Extra :
Similar mech for villages