Hope this helps a few people. Our game had become so bug-ridden, and having Sims getting stuck [especially in bed] all the time, there was no point in playing any more.
PART ONE - Un-instal from your Mac.
1. Finder > Documents > Electronic Arts > The Sims 3. Copy that complete folder to your Desktop - it takes up to 5 minutes. It should be in the pop-up from your Dock. That will contain everything you had in your game. Don't lose it!!
2. Finder > Go > Applications > The Sims 3 > The Sims 3 Uninstaller. Double-click, and don't be afraid! You get the option of which TS3 Application/EP you want to uninstall. I took it one at a time [having been bitten in TS1 and TS2 for doing it in the wrong order] and uninstalled the latest first ... and then worked back to the original TS3. Easy-peasy, everything has gone. At this point, hard drive rattles with confusion! If you have the Apple Time Machine, this may be a good moment to force a backup, and have a cup of coffee or something ... a lot will be happening on the drive.
PART TWO - Install The Sims 3.
Right ... all CDs to hand, with the manuals with the Product Key printed on the back cover. If you have lost them, seek help elsewhere in the Sticky part of this Forum.
1. Install TS3. I'd forgotten how un-intuitive it was. Double-click on the installer button in the bottom right corner. Then make a cup of tea/coffee, Dinner for 4, and walk the dog. When it's all over, close the install panel [why do I have to do that?] and eject the disc. At this point you will [possibly] notice that there is no Electronic Arts folder in Finder ... don't panic, it will happen the first time you launch the game. Oh, and no icon in the Dock either ... you will make that will happen later.
2. Install WA EP. While that loads, build new garden furniture or do BSc in Computing Sciences. If you want to stare at the screen, you will see that the EP patches the original TS3.
3. Install AMB EP. Don't blink, or you'll miss it! This takes a few minutes, including patching WA and the original TS3.
Continue if you have NL, or Stuff Packs.
4. Place latest Icon in Dock. Finder > Go > Applications > The Sims 3 ... drag the latest EP icon into the Dock [it will copy automatically].
5. Phew ... getting there. You still have your latest EP in the CD drive, yes? Good. Double-click that, and will tell you there are Patches available. Clicky-Yes-Thing, and while waiting complete your MA in Serbo-Croat culture. That took a good 30 minutes, which is a bit unfair on Serbo-Croat culture which is far more complex and time-consuming.
You now have re-installed the basics of TS3 with your EPs. You have also lost at least 2 hours of your life, but your Sims are safe [see Step 1].
Now is also a good time to run a Time Machine backup, doing that long-wanted BSc in Astro-Physics. A LOT has changed on your hard drive, so give your Mac a chance to keep up.
After an hour or so, you can now [hopefully] launch a "Vanilla Game". Oh ... when you are in the Launcher, you won't see any of the Downloads you got from the Store. This is where you use your Backup files ... you did save those, didn't you? Open the Backup folder [you did save it all, didn't you? See PART ONE], open the Electronic Arts folder, and drag across the backed-up contents of the folder called "Downloads" into the EA "Downloads" folder. More magic!
We then launched a new Vanilla game with any old Sim, and it worked fine ... including the Adventures Board in France. At that point, you will find [magically] that Finder in the Dock now has the Electronic Arts folder ... cool, huh?
Next instalment later, when we start importing our saved data ... and legacy Sims. Tomorrow may be a bad day!