Apple’s “Let’s Talk iPhone” announcement revealed incremental rather than revolutionary advances to the iconic smartphone.

While many people will no doubt buy the iPhone 4S when it becomes available on October 14 (with pre-orders starting on October 7), those who already own recent model iPhones and other higher-end smartphones have reasons to wait for something better.

Sure the iPhone 4S packs some new, amped-up features and software, but on the outside it looks just like the iPhone 4. Beyond those Apple enthusiasts who feel the need to purchase everything the company releases on day one, or Sprint subscribers who can finally buy iPhones of their own, the big question is whether the iPhone 4S is really worth buying.

The answer depends greatly on your situation. Here we detail three reasons why you should buy an iPhone 4S, and three reasons why you can live without it.

Why it’s worth buying an iPhone 4S

1. Siri – Your iPhone with a brain

Arguably the biggest news of Apple’s announcement event is the release of state-of-the-art voice recognition technology found in the Siri Assistant, which will be available exclusively to iPhone 4S customers. Siri marks the true beginning of deeply integrated voice control and will change how we search and process information by speaking rather than typing into our phones.

Siri will be integrated deeply into all kinds of apps, and it is supposed to be powerful enough to understand your natural language and meanings. On stage, Apple’s software guru Scott Forestall asked Siri, “What’s the weather like today?” The service responded by pulling up a weather forecast. It can also do things like take dictation for text messages, read back emails, set reminders and give you directions. Basically, Siri sounds like it will be a great sidekick on the adventure of everyday life.

The app will also keep track of you and learn from your patterns and behavior, so it can better personalize the answers it provides. Even better, you can use Siri with the keyboard for those moments when you don’t want to look like a crazy person who thinks his or her cell phone is alive.

2. The power of the A5 chip

Apple first unveiled the A5 processor chip back with the iPad 2, and it is the reason that the iPad 2 is so much cooler than the original. On the iPhone 4S, Apple boasts that the chip will provide an increase in graphics speed of seven times more than the A4 chip, found in the current iPhone 4. That means games will run better and will be prettier, as will videos.

Apple teamed up with Epic Games to announce the upcoming Infinity Blade II to show off the power of the A5. The original Infinity Blade is one of the best showcases of the power of Apple’s iOS software. Both companies promise an even more beautiful, seamless experience. Early screenshots suggest the game will look as good as some of the stuff we’re seeing on the current generation of video game consoles like the Xbox 360 (though that might be wishful thinking). If you’re a serious gamer, you’ll probably want the A5’s power.

3. A big new camera sensor

A while back, Flickr released some numbers that suggested the iPhone had become the camera most used by the photo service’s users. Apple has increased the resolution of the iPhone 4S’ camera to 8 megapixels, which means there will be a lot more information carried in each of the images it captures.

This doesn’t necessarily mean better photos, but the iPhone 4S will certainly be capable of producing better images than its predecessors. Some users have already demonstrated that in trained hands, an iPhone can produce videos and images that are at least comparable to what can be created using better equipment. Expect those possibilities to increase with better hardware. For phone photographers – amateur and professional alike – the 4S should make it even easier to capture great pictures. The iPhone 4S will shoot faster and even take photos from the lock screen.

Why you should avoid buying an iPhone 4S right now

1. An update that’s not much of an update

If you already own an iPhone 4, you would probably not get a major bang for your buck by going for an iPhone 4S upgrade. Granted, the A5 chip is nice and Siri telling you what restaurants you’ll enjoy can be fun. But is that worth $199? Many of the hardware upgrades make for a better deal to customers considering a switch from devices running on Google’s Android operating system or upgrading to the iPhone for the first time. But they’re not really geared for current Apple fans.

The iPhone 4S can only do a few things that the iPhone 4 can’t, and with the release of the next version of Apple’s mobile platform, iOS 5, the current generation iPhone is going to be receiving a whole lot of awesome new features as well. Siri, while sounding very cool, is still in the early stages of release. It will likely be a lot better by the time the iPhone 5 rolls around.

2. A5 chip isn’t a must-have for gaming

While the A5 chip does seem to be a big step forward from its predecessor, if the iPad 2 has taught us anything, it’s that the new chip probably won’t bring a big torrent of new games that won’t work with old hardware. It has been more than six months since the release of the A5 in the iPad 2. Yes, some games have been optimized to work with it. But many, many more don’t need the chip, and most apps are still compatible with iPads. So not having the A5 probably isn’t going to mean missing out on a ton of new games.

Even Infinity Blade, which will look “best” on the iPhone 4S, isn’t going to require players own the newest iPhone to play it. And you can bet it will still look pretty great on your iPhone 4. It’s doubtful developers are going to start adopting the A5 and its capabilities at the expense of all the iPhone owners who still own older hardware. If you’re extremely serious about mobile gaming, consider an upgrade; if not, waiting won’t be too big of a deal.

3. A bigger and better iPhone next year?

So the iPhone 5 didn’t grace the stage today, but iPhone fans for whom an upgrade isn’t cheap or convenient with their carriers, that may be a good thing. It’s been 18 months since the release of the iPhone 4, and it’s not a bad bet to figure that Apple could go back to announcing iPhones in the summer during its Worldwide Developers Conference in June next year. If that’s the case, it’s really not too long a wait for the next iPhone – which will almost certainly have a redesigned exterior and better internal hardware to boot.

If you can stand the wait, you will be rewarded with a Siri Assistant that should be out of beta and probably will work better than what iPhone 4S owners will be getting. By then, Apple will be planning all kinds of new features to go in its next device. Many rumors are pointing toward a bigger screen, for example. While the look and feel of the iPhone 4S is still that of the iPhone 4, the iPhone 5 will be a wholly new experience – if you can wait that long. But still, if you have a perfectly good iPhone, especially if you purchased one when the device was released for Verizon, why shell out for an incremental upgrade?

Verdict: The iPhone 4S is not a must-have device

The iPhone 4S really seems like it is geared toward new iPhone users rather than existing ones, and if you’re a Sprint customer or someone who’s been on the fence, this is a great device to grab. It’s better than the iPhone 4, with more capabilities, a world phone antenna setup that allows it to work on any of its three carriers, and speeds comparable to some of the “4G” offerings other devices boast. Those are all reasons to grab an iPhone if you’ve always wanted one.

But the experience probably won’t be vastly different if you’re already using an iPhone 4. Data speeds will be faster, games will look sharper and Siri will give you advice. But it still seems difficult to justify a minimum $199 premium for any of those features.