Yes, the iPhone 7 is a worthy successor to the iPhone 6 because he continues to show Apple's ability to evolve. One of the iPhone 7's main improvements is the wireless headphones. Everything is becoming wireless, so it only makes sense that the iPhone would keep up with the times.
The iPhone 7 will likely sell out the iPhone 6 or at the very least many people will want it. But it removes a few key features, namely the abilty to plug in standard headphones that make it easy for the average user to use. It is not a substaintial improvement.
The upgrades to the iPhone are to the point where they are so frequent I think Apple is intentionally holding back new technology in order to place it in a new version of the phone that people will line up for. Based on what I've seen, the upgrades this time aren't worth the cost of the upgrade.
No, the iPhone 7 is not that big of a deal. Sure, it has a few more features and looks different, but a phone is a phone, and at this time there isn't much that technology companies can do to improve on the design. Perhaps it's time for new inventions rather than the same old stuff rehashed.