Minor update on this; I finally went through the hassle of redownloading everything about a week ago. Once I confirmed everything was working properly, I copied the entire Sims 3 folder as a backup onto a separate external drive. So far, so good?
Well, today I opened up the game and all my content was once again non-functional. I deleted the broken Sims 3 folder, and replaced it with the backup from the external drive. However, the result was the same. The game continues to not recognize any of my installed content. At this point, I'm pretty much resigned to the fact that there's no official way to access the store content without it disappearing anymore.
