Yes, yes you should!
Admittedly Sims 4 is out soon, but there will be a LOT more you can do with Sims 3 vs Sims 4... at least until they get a few expansion packs out the door.
Yes, I'll admit, I won't be switching to the sims 4 for a while because I haven't done nearly everything I can do on the sims 3 yet. However, I do feel I'm behind because everyone has been playing the sims 3 for years. And, I'll continue to be behind because I'll wait until I'm bored of the sims 3 before making the switch, otherwise I will have wasted money on all the games I've purchased recently. If I was just now getting the game I would wait for the sims 4 and be on the same page as most players, rather than behind.
But you're right, it will take time for the EP's of the sims 4 and those are what add a lot of fun to the game.