All except the wood market upgrades become useless later on in the game after hunts and mines are gone. The food trickle card gives you an effective 53 villager economy (using Mills for food gathering rate) instead of 50. That's why it's more useful late game than 3 villagers.
It's also, against many civs, more useful than 3 villagers early game. Against Russian, Aztec, Sioux, Iroquois, Ottoman and Spanish rushes, when a large number of your villagers will be holed up in the TC or forced off hunts, you'll stil get atleast some food income.
Basically, the short term advantage is in the uninterruptable income, and the long term advantage is in being able to go slightly beyond the villager cap.
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