I need gameplay ideas!

I feel like I've done everything in TS4.

Well, I'm still not sure what exactly you mean - all careers? Aspirations? Have you tried a lot of Challenges?
I'll leave this aside (for now) and present some other ideas instead.

1. If you've played other Sims games before, why don't you try recreating your favourite family that you made? Or maybe you still remember that one save that unfortunately got corrupted so you couldn't keep playing. Why not give a try in TS4?
2. In a similar vein, why not try recreating some premades that don't appear in TS4 (or any other games other than the one they debuted in) and play out their lives anew? Maybe it'll even be the start of a great new legacy!
3. This is a very big project, so this probably isn't for everyone, but have you ever considered creating your own save from the ground up? You can rebuild the worlds, renovate lots or leave them as is and simply create new households. You may think you have played out every idea you ever had - but others may be looking for that one storyline or household you came up with. What seems boring or overdone to you may be something new and exciting for someone else. Generally, I just think it's fun to share saves with others. :)