The Antiques dealer is good. I have no problem with the timeframes for auction, breakdown or sales. If there were no time constraints then it would possibly work against the goal as a long time game. If the inventory was filled over years, it shouldn't be a problem to empty it over years.
If you can empty the inventory to fast, there would be complaints by players, that they do not get enough useless stuff to sell for the dealer.
What should be considered is that the same item from different eras should give different amount of Trade Coins.
For example Future Era SoK should give slightly more than High Middle Age SoK.
Same with Terrace Farms, but there I am unsure if it should be in reverse, because
1. the population requierement is lower in lower ages
2. High age players can get new high age Terrace Farms, but not lower age ones, which makes them more valuable.