The pot, state and plant markets by themselves only boost happiness in a radius of 25 by 0.3 to 0.1 at their exterior. ie not much better than adding a villa which has a range of 22 and boosts to 0.2 at its far radius.
But they also have a base capacity of 6. Placing all 3 in the middle of a hovel might be interesting. Not sure what happens as they are staffed, or how far the extra capacity can be pushed.
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After investigation, you can't boost the capacity, and having it staffed doesn't boost any effects. Placing them in the middle of hovels partially alleviates their misery, but not enough to be worth doing.
And the benches don't seem to come from only Universities. Placing meadows next to some hovels created benches on the hovels. Yet they were still unhappy.