Well I'm sort of the opposite to you: I upgrade my devices when I feel the device needs upgrading and not otherwise, and don't let any corporation try to push me into signing new deals to lock me in for longer. So personally I'd ask "do I need to upgrade?" and if so "is there anything I actually fancy?"
But assuming you are set on upgrading, you clearly like Samsung (though there are other manufacturers out there). If you ignore the whole "it's new" thing and just look at the device itself would you actually prefer the Note 8 to the S8, and if so is this because of any feature that's specific to the Note? If your answers to both questions are "yes" then I think our job is done.
If not, then your options would be to buy an S8 (so what if it's 6 months old? It's the same processor, probably the same camera sensor, etc) or wait for the S9. Will the S9 be better? Nobody can say, because right now we have no information about it. The marketing people will say it's better, because that's their job, but I've known cases from all manufacturers where I've thought "actually I preferred last year's device", so there's always some element of risk in waiting for something which may turn out not to have been worth the wait. Really only you can decide on that.
