I'm actually going to point to your own analysis a little, BaruMonkey. You talk about the upside of shanty town - mitigating the risk of not having actions in hand to start your engine - but NOWHERE in your post did you mention the drawbacks! Shanty town can either be +2 cards, +2 actions, which is like a Level 2 city, better than a $5 card... OR, it can be +0 cards, +2 actions, which is WORSE than every single village in the game! Your post talked ONLY about the upside, whereas you have to weigh the upside against the downside, and estimate how often you'll get one or the other.
Shanty town is better than village in the case where you have no other actions in hand. However, if you have the sort of deck which consistently doesn't have any actions in hand, why on earth would that deck need villages at all? If you rarely have two actions in the same hand, then +2 actions is pretty useless! +2 cards is still nice. On the other hand if you DO have multiple actions in hand, then shanty town is just +2 actions, no other effect - and that's a pretty terrible card, that's worse than Native Village and Hamlet. I mean, it'll do as a village if you really want to build an engine and there's no other villages around, but it's pretty bad.
And if you draw Shanty Town with ONE action in hand - well, then that shanty town literally did nothing for your hand, it was a dead card.
It's sort of a beginner play because Shanty Town *appears* to shine in decks that are neither here nor there. In a good engine deck, you should have enough villages and actions that you basically always draw multiple actions in hand and so shanty town is bad. In a Big Money-ish deck, you should be avoiding collisions, and so you don't want villages, because it's so much more likely to draw one shanty town and one action rather than one shanty town and two actions. So really, Shanty Town can 'collide' with actions in much the same way as a terminal action does, it's a dead card if you draw it in the same hand as another action.
There ARE cases where shanty town is a good card. For example, in a deck with mostly money, a small number of shanty towns can act like cheap Laboratories for $3. But only as long as you don't get too many, because if you get too many then they'll start colliding, and two shanty towns in one hand just replace themselves. And really, if you only use one laboratory in a turn, it's more of a Moat than a lab... In a deck with only cantrips, a single shanty town can also act as a laboratory, not bad.
But when you actually want to use Shanty Town as a Village and use it for its +2 actions? Not good at all. Sometimes necessary anyway, because, well, sometimes the other engine cards are good enough to make up for a bad village.