We hear a few things consistently:
1) Providers have switched from "free upgrades every 2 years" to a plan cost and a monthly phone cost, so people now really know how much their phone costs--and many would rather save the $30 a month than upgrade their phone. This started with T-Mobile a few years ago and now is how most phone plans work. This is having a huge impact on people's desire to buy new phones.
2) iPhone 5/5C/5S users have no desire to upgrade to a larger phone. The SE is going to solve some of this, but it'll more likely be a scenario of "I dropped my 5S in the toilet and it's completely dead, so I'll upgrade to a SE instead of dealing with the hassle of finding a legit used 5S." I don't expect to see a huge push toward the SE from current iPhone 5 users.
3) Repairs are so cheap, so easy and so effective. It's $79 for us to fix an iPhone 5/5C/5S screen right now, and we can fix it in less than 30 minutes typically. No reason to upgrade when your old one works just fine and you can get it fixed cheaply.
Interestingly, the SE screen is 1:1 compatible with the 5S screen, so the SE is coming out of the gate being cheap and easy to repair as well. I'm typically recommending the SE if people really want a new phone.
We also ask customers about 3D Touch (the new feature on the 6S/6S+) and if they're using it if they have a 6S. 99% of people have no idea what it is or how to use it. They bought a 6S/6S+ because it was pink. Yep, most of the 6S phones we see are rose gold, and that seems to be the #1 factor driving sales of that line. If they don't care about the pink and ask me what phone I recommend, I recommend buying a refurbished 6 over any of the 6S line. (We don't sell phones, so I have no horse in that race at all.)