Suggestions to keep the game interesting I’d say try things you don’t normally do/ that are out of your comfort zone. That’s how I found my play style (aka found out my preferences. I always tried the family approached in TS2 but never got past second gen because I got so bored, now I know why).
I started by creating a sim with nose, hair colour, clothes, traits etc I rarely used, if at all. Just to explore. I made him a writer at the time because I wasn’t really playing that path before and tried different things with this sim. I’ve played him on and off for three years and although the traits are getting a little old (childish, insane and geek) he is still my favorite sim.
So try something you aren’t doing right now or are not really comfortable with. Don’t like vampires? Play as one. Always have kids and then get bored? Only adopt (if you just can’t help yourself) but focus on a career you usually don't play or only play a romantic sim with commitment issues that you have break up with the current partner as soon as he gets a whim to. Play as a detective if you don’t normally do that. Finish a collection.
Since you said you usually don't complete aspirations, create a save with aging off and do just that. Use your favourite sim (if you have one) or create a new one.
Play aging off in one save if you always play with aging on and vice versa. It gives you a new perspective.
Set “rules” for your sim, like never turn down a social invite or never initiate flirting with anyone (my sims I try that with usually ends up gay, I think it’s because they use the enchanted greeting at random sims when their charisma is high enough).
You could try challenges as well. The only one I have enjoyed and stuck with was the time lord challenge. It’s a doctor who challenge but you don’t have to have watch the show in order to play it, I’ve never seen an episode.
You could also set your starting money to 0 and see how long it takes for you to get enough money to build a house.