Depending on how long “soon” is, I’d say no. There’s not a lot immediately different as a large part of the changes are “under the hood” as opposed to the total UI overhaul of iOS 7. Unless there’s a feature you have to have, there’s no rush to upgrade, in my opinion.
As we see more developers using extensions, and the real launch of Handoff/Continuity to pass work to and from the Mac (likely next month), iOS 8 will be more of a “must have”. Also, eventually, app updates will likely start requiring the new iOS version as the developers start relying more and more on its features.
Thanks much for your replies ;) I think I’ll pass, since I’ll (hopefully) be getting the new phone in a few weeks.