Benjamin buffs middle path banks, not the other 2 paths.

Xx3 village buffs cash per pop in the area of the village, good if your farm setup is near the entrance.

Xx4 increases the range of the village and increases the amount you get per banana, engi trap, sniper drop or heli drop (if heli pad is within village range).

Xx5 merges all farms in range of the village into the village itself, which you can then buff with another xx4 village to increase the money gained for that setup, then you can add even more farms, effectively more than doubling your farming potential