Real Estate Trader/Broker
With the addition of Carla's expansion that requires the older expansion requirements, perhaps introducing another intermittent character like Mr. Merriweather would be helpful.
The new character could be unlocked when a player starts needing the second level of expansion requirements. This person (for now, the Real Estate Agent) can occupy a plot of land next to the Farmer's Market, and will drive up to the farm and stay for a few hours (maybe 4, like the Balloon). Older players can trade some of the new expansion papers for older ones or vice versa (maybe with an additional coin fee), and newer players can trade some of the older papers for the newer ones or vice versa.
I don't know about other players, but I have mostly been receiving only the newer (2nd and 3rd level) expansion papers and only very rarely the 1st level papers. An option like this would be very helpful.
This is a great suggestion! Would love to see something like this in the future!
If a Real Estate Agent/Broker is not a possibility, then perhaps the prizes in the Leaderboard events can be changed each event? For example, one event would offer Expansion Permits, the next one offers Land Deeds, the third event offers Old Maps, and then the cycle repeats.