If they make it better for the reader, they can potentially raise the price. If they can make it cheaper to produce, they can potentially increase their profit without raising the price.
Usually on balance this falls somewhere in between -- more value for less money for the consumer, and more profit on each marginal unit of production for the producer, which is how technology progresses across most consumer goods.
Yes, but they're not going to pass on costs from not using a voice actor. They're just going to charge what they normally would have, and not worry about having to give so and so a cut.
Niche stuff has always been economically viable. Niche stuff also tends to get publisher support. Realistically these days the only reason why books don't have an audiobook format is due to not wanting to support Amazon/Apple, or because they just don't want it. Voice actors literally are not expensive for audiobooks. You can absolutely afford one if your tiny $9 book hits more than 200 copies.
Unless you're talking about illegal niche, in which fair but I highly doubt stores are going to accept those. All generation helps with is content that will be free.
I think you’re underestimating how much work goes into hiring and producing something. Making it more self-service will go a long way toward making it more accessible to small creators. And my impression is that many books don’t sell 200 copies.