One way - probably the only one so far - of raising difficulty in the game is to play challenges. There are plenty of challenges, and there's this
thread with a list.
I've tried a few of those challenges so far and your first example where you're not allowed to change your sim's aspiration whenever you like it is part of all challenges I've tried so far.
The idea with the lot trait sounds pretty cool, too! I can't think of a challenge where this might already be a rule but you could start your own challenge with it :)
I wouldn't even open the game once anymore if I didn't play challenges. That's the only way for me to play the game and enjoy it. Plus I write stories about the challenges which also helps to keep me interested.
But all this depends on what you expect from the game, of course.
If the challenges - or creating your own - doesn't work for you, maybe there are mods out there which add more difficult things to the game. But I wouldn't count too much on the feature being added by the devs :/ Mainly because it has never been in a sims franchise (or I have never heard about it).