The answer to your first question depends on whether you want to read about speculation that might actually be true, or just read anybody's pulled-from-their-backside claims. Very different sites.
At this point I think it would probably be best to just wait. One week from today, September 10, we'll know the whole story (press invites
went out today).
If this event runs anything like almost every previous one ever, about 60 percent of the rumours will be true and about 40 percent of them will be false. I personally think we'll get two iPhones, the 5S and 5C; the 5S will have a fingerprint sensor, new processor, 802.11ac and better camera but otherwise be basically the same as the 5.
The 5C will likely be available in an array of colours, and essentially be similar to the current iPhone 5, though there may be some omissions. I personally think the iPhone 4 and 4S will finally be retired, replaced by the 5, 5C and 5S. I also think we'll get the formal release of iOS 7 for all current* iOS device owners (iPhone 4 and up, iPad 2 and up).
I don't think we'll get NFC, new iMacs, new Mac Pros or anything not directly iOS-related. We might get some news about things to come, however. Naturally, I could be wrong about any or all of these predictions.
As to whether you should get the new release, that depends a lot on whether you think the (likely) upgrades to the iPhone 5S are worth it, and whether your carrier will permit it (I'm assuming you're on contract). I have a hunch that most iPhone 5 owners will be happy enough with the changes in iOS 7 to hang on to their phones for another year until their contract ends, then upgrade to the iPhone 6 or whatever. People on iPhone 4S or 4's, however, will have much more motivation to upgrade.