I think I'll wait a bit until prices come down a bit. I waited a few months before pulling the trigger on the S8+ and got it basically for OnePlus prices. That's awesome value for a Samsung flagship. This S8+ should serve me perfectly fine until the initially skyhigh S9 prices settle down at least a bit.
That's what I always do. If memory serves, I got my S8 for £450! It had only been out for a couple of months at that point.
Tbh I'm really happy with it. I doubt I'll change unless a bargain comes up.