I don't know why your game keeps getting corrupted. However, one fix that has worked before is to ... copy the .nhd file from an old save into a new one. This means choosing the same world to start a new game. Use "save as" to save that pristine, untouched new world. QUIT the game. Then, go into the save folder in the sims 3 folder to copy the old .nhd file (from the played save) to the new (unplayed) save.
In order to try to avoid future corruption, you can rename the old sims 3 folder and let a brand new folder be created when you launch your game. Go to the options in the game and change the settings to your liking turning off the auto memories and the auto spawning off pets, supernaturals, weather, full moon cycle, etc. Then use "save as" to create a save file. Quit your game.
Go to the old sims 3 file and copy the .nhd (neighborhood) file from the your oldest, non-corrupt save in the save folder to your new sims 3 save in the current sims 3 save folder.
You will also need to copy the .ebc files from the old dccache folder to the new one for any store content you may have installed. Sometimes store content such as venues install into .dbc files as well, though mostly they are for other custom content. (You can check to see what is in any .dbc files by moving out the .ebc files and using the launcher to see what it is them, but using the launcher to delete items from any of the files in the dccache folder does not actually delete them. It just keeps you from seeing them.) The reason for simply copying the .ebc files is to try to avoid bringing over any possibly corrupt custom content. Along with copying the .ebc files, you need to copy over the ccmerged file from the dcBackup folder. NOTE: If you use a lot of custom content, you will need to decide if you want to copy over the .dbc files too OR to just reinstall what you know is safe.)
Installed store content also creates other files. Store venues that show up in your game bin for placement get a file each in the library. (Library files are "numbered" not "named" so you can only tell what they are by the date they were created.) Installed worlds will have a .world file for any world you have installed. (You do not need the world cache files, as cache files will regenerate when you load a game. They just take more time to display everything the first time you load them.)
If you have saved styles in CASt, such as unlocked stencils or favorite recolors, those are in a file called userpresets. So that file would be another you might want to copy over.
You might also want to copy over library files (for any store venues that installed into the .ebc files OR lots (and families) you may have saved to the bin. This is not needed for changes you've made, such as building and landscaping directly on lots.
After copying over those essential files, load up your game again. This time, when you load the save that you made option changes to earlier, it should look like your old save. (Of course, if you didn't copy over any custom content, there will obviously be some strange replacements.)
So, long story short: copying the .nhd file from an old save to a new one should keep the look of everything, but possibly avoid the corruption.
