There is a really nice guide made by someone with a lot of experience that details how to make coins. Basically, be active on the forum, post responses and make relevant threads that attract interactions.
If the update takes longer than 3 months, I instantly assume the developer has no idea how to prioritize and plan work or they are maliciously milking the funding. Especially if they have a patreon and demand people pay them monthly, while giving nothing in return.
What exactly do you mean by "large increase"? Barely anything at decent quality outside the JP market, and those are censored. I wish I had this problem, one of my favorite genres.
I don't get it, why even play a game if you skip the dialogue/story? Just rip the art if that's all you are interested in and you are done. Renpy, Unity, HTML, all can be unpacked. Just watch the pics, fap and move on.
It's a cheap/easy source of assets for someone who wants to tell a story. Games like The Company tried to move away from RL porn images/clips and supporters rejected it, because they like the result.