Playing on PC gives me the advantage that I can just wait for the bonus items to be modded into the game. But so far, I've never felt the need to look for such mods or cc. They're really not that special.
The only bonus items I have are those from Cottage Living, which I bought shortly after its release. Not because of the items, but because I really wanted the pack, and I don't regret buying it at full price. I can hardly think of any type of bonus content I'd want so bad that I would buy a pack early when I wasn't planning to do that anyway.
Edit: I forgot to say, Horse Ranch is another one of those packs that I really want, so I'm probably going to buy it early and get the bonus content. But again, the bonus content itself is not the reason.
