I am on the same boat, but I have an iPhone 5. I could buy an iPhone every year, but they are so expensive in Europe that I find not acceptable to spend such a high amount of money on smartphones.
However, because I actually can afford it without any problems, I am not sure if I should buy the 6 or wait for the 6s. I lived with my 5 until now, so I could wait. But last week I saw a 6 and I actually want Touch ID, better LTE support and other features.
It's a tough decision. I was a bit disappointed by the fact that the 6 has just 1GB of RAM (as my iPhone 5), and was also disappointed about the lack of an higher resolution. If I buy the 6s, I will certainly not buy the 7, and I doubt that the 6s will have more than 750p.
But regarding to the 5s, I think it is not worth the upgrade to the 6. You will have very little performance improvements, and you still have Touch ID on the 5s, and the camera is also great. But at the end it's all about money. If you can afford and you don't mind spending money (I can afford but I do mind spending that kind of money), go for it.