I was in the same shoes as you are. I was offered an upgrade to a 5S, in case I was to renew my 2 year contract and pay an extra $10 every month.
I told them that I was not interested, and called their customer service to cancel my contract. They offered me all sorts of offers in order to keep me as a customer, and by the time I was done I received a 30 % discount on my line and signed up for 2 more years, while keeping the phone I have (4S).
Honestly, the 4S still works good. It's not blazing fast, but it still has decent performance, a good 8mp camera, HSDPA, and a nice solid feel. Seeing as I'm a student with limited resources, and tend to hold on to my devices for quite a while, I want to get the most out of my upgrade. In my case, I don't particularly care for the A7/M7 and TouchID. I will much prefer the next upgrade which is said to bring a larger screen than the 5S (which is what I lack the most).The A8/M8, TouchID, et.c. will be great bonuses. Mostly I look forward to a new design though, the 5S is way too similar to the 4/4S, which has been around since 2010.
It is a bit tempting to get the 5S, sure, but I'm sure waiting for the iPhone 6 will be worth it.