Fresh Restore while Retaining App Data?

I had a jailbroken 3GS and did a lot of tinkering with stupid jailbroken stuff.

I always just used it as is and it worked okay. When iOS4 was released, I installed it and killed my jailbreak.

Despite me "breaking" my jailbreak, some of my tweaks remained(such as my custom carrier name), I don't even want to know what kind of important files were tampered with.

When I purchased my iPhone 4, I just restored from a backup of my 3GS; seamless transition, cool.

Well, my iPhone 4 is starting to be a big laggy, I still have a custom carrier name is that now unmodifiable, my battery seems to be draining quicker, etc

I'd like to restore fresh, but I don't want to lose all of my app data.

Most importantly, I'm interested in retaining my SMS's, and my game data. My contact stuff, etc are all synced with my Mac, so no big deal, but what about the game data?

Is that stuff backed up on my Mac, so when I drag them onto my "new" iPhone, my saved data will go with it?

If not, any suggestions? Thanks in advance.

 

Id even be happy if I could just retain all my text messages. I don't really want to jailbreak it again. I don't understand why apple wouldn't just allow you to restore individual apps.