The tropes do get old, but not because of what they are. They get old because of what they always fail to do. So when a brother stalks and molests his sisters, they follow the same route:
1. Sneak into your sister's room and maybe touch her, then over time do more to her
2. If she wakes up, you usually have maxed out luck stats and get out before she sees you (nevermind that her clothes are sticky, disturbed or missing)
3. You develop a sexual relationship openly, eventually, so it isn't a big deal anyway
What they always fail to do is give power to the sister, over her brother, when she catches him in the act. Maybe she is twisted herself, so she blackmails him or makes a bet that he can't trick mommy into bed. Maybe he goes all the way one night, she wakes up in the middle of having an orgasm, and it haunts her until she gives into lust. We don't want permanent consequences in our incest game, so there will need to be a twist that wins her over or awakens some dark fetish she always had and now has power over her brother to make him do gross things to/for her. Then it builds into a competition between them. They get more daring and incorporate other family members, or a friend that was studying to become a nun, into their debauchery.
Take the trope of mother and son dinner, turning into a wine drinking fuckfest. Usually, the MC is also boning his sister, but keeping it from his mom, and vice versa. A good variation to add to the trope, is that maybe the wining and dinning is an attempt to butter mommy up so she won't freak out when they confess their relationship. She also feels attracted to her hunk-of-man meat son, so she can't get mad and become a hypocrite. Emotions run high, the wine runs dry, someone says something irredeemable, and suddenly shouting turns into a hardcore threesome. Then daddy walks in, back from his overseas business convention...
I think the tropes are good. I just think all of the unexplored questions, or scenarios that are obvious but always ignored, or the lack of any sexy consequences is what gets tiring.
That was
Uthuriel's main point. Complaining about tropes isn't helpful for devs if you aren't offering up your own ideas to add something new. Maybe these scenarios are too dull for some people, or not enough of a change. But I would rather offer up new ideas along with my gripes. Especially since we are in a position where what we say is very likely to be seen by a game Dev.