I mean, anyone can upgrade to iOS6, that's the core of the phone. The bigger screens are ugly, not gonna lie. LTE I don't care about. I'm thinking that the smaller dock connector so that the headphone jack can go on the bottom is a good idea, but I've already gotten used to it being on top.
I've never had to think about if I wanted to upgrade before...
Headphone jack at bottom is a BAD idea. There are thousands of car docks that use aux connection as well as your 30 pin connection to play audio. Hopefully pretty soon 3rd party accessories are made that take care of this problem.
Big screens are ugly... how? Its more of the same that you already have. I personally think 4" is perfectly big enough for a person to use without it being too big in your hands.
When LTE goes mainstream (as it has in my City) you will care about it. $100 bucks that some time before the iPhone 6 releases you will make a post saying "iPhone is just too slow Apple needs to step up their game."
The two-tone design we've been seeing is kinda hideous, but with a case, it wont be that big of a deal.
Anyone can upgrade to iOS 5, but they miss the functionality of many features, like Siri for example. You may not use it at all, but for me, who uses is multiple times daily, it makes my life a whole lot easier when I can simply tell my phone to message someone, or call someone, or to remind me about this, or to wake me up in half an hour, rather to have to manually enter in the data myself. You paid money for the phone, use it how it was suppose to be used.