TS4 needs a difficulty system.

I agree that a difficulty setting would be good, but honestly, I feel that fixing the difficulty should be more than just a matter of imposing negative elements on the player. I made some suggestions on improving the difficulty a while ago, with my main focus being on making it so toddlers and kids actually need their parents to take care of them instead of them being able to perfectly survive on their own while their parents just do whatever and ignore their existence. I suggested once a special refrigerator where kids can't just grab quick meals from the fridge as they please and need their parents to cook for them and remember to have leftovers. I suggested adding toys that don't cause toddlers to learn/level their skills so that they'd need their parents to teach them. I thought of making it so job tasks are less repetitive than just "practice this thing, level up this skill, get this emotion", etc. I also feel it should be way harder to adopt a child, like the parents should have specific skills they need and maybe they need to be at a certain level. I feel that things like this will make the game naturally more difficult, not to mention more realistic.

As for your points, well my current issue with aspirations is that I think they need to be more than just tutorials of new pack features. I find them easy because they're literally just click-lists made to show off new pack features, rather than feeling like an actual desired goal for a sim's life. A lot of them seem really repetitive too. I do agree that I think it's weird that you can just change them on a whim, and personally I would make it so they can't be changed unless completed, but I'm sure there are players who like that they can jump from aspiration to aspiration whenever they want so, I feel like they'd never change that.