The Sims 3 Crashing!

There's nothing you can do; there's no solution to most Mac crashing.  Crashing in CAS (without having any CC or mods) is most likely to due to the fact that CAS requires a lot more resources/memory than playing the game.  Memory with the game is handled terribly with Mac Simmers because the game uses Cider.  Cider tells the game our systems are running a 32-bit WinXP system with only 2gb of RAM (even though are Mac specs are better than that!) so that it's "compatible" for our system.  This means our games freeze and crash a lot more often than Windows players because it's easy to use up all the memory it thinks we have available.    

I'm not sure how much troubleshooting you've already tried, but here's some advice:

If you actually want to "play" the game as it's supposed to work, then get a PC or Bootcamp & Windows for your Mac. The game is not natively written for our systems (I have a mid-2009 Macbook Pro). As long as EA uses Cider, a "wrapper" for the game that enables Macs to play Windows games, it's going to crash with memory issues.

Do not follow EA game advisors' advice without taking into account that many times their advice is wrong for Mac users and can harm our systems. Just use common sense when it comes to their "advice."

Here are two good posts from the Sims 3 Mac forum that have a couple of useful "band-aids" to get the game to work temporarily:
-- http://forum.thesims3.com/jforum/posts/list/658546.page
-- http://forum.thesims3.com/jforum/posts/list/611723.page

Also, it's better to play in Windowed mode so that if it crashes, you don't have to restart your whole computer.  When it freezes press Command - Option - Escape simultaneously to pull up the menu of applications you have running and force close the Sims.