well the only things i'd buy from the exchange would be a mansion or 2 
out of the highest recommended list, so i'm sure they would be okay, right?
Sticking with the highest recommended or highest downloaded items is a good plan. I do similar myself. But exchange items can foul up your game. See below.
To be clear, the Store and the Exchange are two very separate things. The only commonality is that they are both hosted at the official Sims3 website.
The EA Store contains items made by EA/Sims3 paid personnel. The same people that make the items for the game and expansions. Some you can get for free and some you have to spend money to get. You spend money to buy points, and then use the points to buy the items and download them.
The Exchange items are all free, but are also all made by non EA personnel. People like you and me. The quality of the items will vary. Some will include custom patterns and content, while others will not.
While the Exchange generally seems to be a better source for player made items, that content is still subject to problems just like other custom content sites. For example, there has been a big problem currently concerning a 3rd party created Doll that can slow your game down dramatically. It was created on another website, and when people downloaded it or houses that contained it, it started attaching itself to other Sims 3 items on their PC and in turn getting uploaded, much like a virus. It quickly made it's way to the Exchange. EA has
specific instructions on how to remove this content from your game should you get infected.
I highly recommend running the game without downloading any custom content for a few weeks, just to see how it's going to run on your computer.
