Agree with what's been said by others.
I bought an SS when it first came out. Used it for 6-months then sold it as I jumped around Androids for a while.
I moved back to a 7 Plus before Christmas and picked up a brand new SS Link for £300. That's £600 less than the S2.
My usage hasn't changed and I can honestly say since my first purchase on release, battery life is way better (used to end on 25%, now 45-50%. There interface is quicker on os3 since it was and I predominantly use stock apps.
A friend has an S2 and in my usage (notifications, alarms, tracking fitness activities) I don't see £600 of added value in the S2. Yes it's a bit quicker and has better battery plus GPS. But unless the battery can track activity on GPS for 5-6 hours and last the day I'm content to wait for future improvements.
Future updates are the question but I'll be quite happy if it retains this performance over the next two years. If that means no major os updates then that's fine with me.