I think we can talk about the virtues of Sims 3 all day. Objectively, it seems worth buying. BUT I still think the bottom line is the OP's computer.
Is it 32 bit? Is it 64 bit with backwards compatibility? How old is it? How long do they think they will have it? Is it Mac or Windows? The OP never answered those questions, and it matters.
If you have an older Mac that isn't updated, you can still play Sims 3. Mine is a 2013, and I managed to hold off updating until a few weeks ago. After I updated, I lost 32 bit support and Sims 3. And now it's looking like I'll need a new laptop soon anyway. You can only hold on for so long.
For now, Windows is still backwards compatible even if you have a newer machine. But for how long? Pretty much everyone else has dropped their support for 32 bit, and games are all 64 bit. Even Sims 4 has always been, and they are dropping 32 bit support in June. So Windows is likely to move along with everyone else in the next year or two. Maybe three if you're lucky.
So, if you have Windows, the question is how much is it worth it to you to spend the money on it not knowing how long you can play it? If you find it for cheap, you might be okay with a year. If you pay full price, then Windows decides to phase out 32 bit, will you feel cheated? If you decide to hold off updating for awhile to extend your gameplay, how long will that work for?
Something else to consider is EA's support for Sims 3. As of right now they support and sell it. But, they don't sell or support 1&2. They gave UC to everyone who already owned it, then dropped it. And they haven't supported 1 in any capacity in a very long time. And knowing that they are dropping 32 bit support in June, and Sims 3 is 32 bit....