It doesn't sound like you are using the computers for "professional" use, so it really is a matter of finances and desire. If the money isn't an issue for you (although you did mention frugal times?) and you won't mind taking a bit of a financial hit should you decide to later upgrade to the next iMac iteration whenever it should arrive, then why not if it makes you happy? But I would ask yourself if you will actually get any benefit use-wise from it or if it would just be a shiny new toy that functions the same as what you are using -- i.e., the Macbook Pro. And if that is the case, will that bother you? It sounds as though it might given your statement that you "really feel you should wait." Personalities are different and a purchase that will bring no end of joy to one person may cause buyer's remorse for another

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In my case, I don't expect I would see any very significant performance gains from my 2015 i7 given my day-to-day use, but I'll have to sink a little money and some time into upgrading my wife's old (2009) computer and use a 3rd party patch to upgrade beyond High Sierra to ensure continued security patches. It may not be rocket science, but my experience with computers (I've never had to open a Mac) suggests that there are any number of things that can go wrong in the process and potential frustrations. At the end of the process we will still have one 5 year old computer and an 11 year old computer that owes us nothing but would probably run pretty well after an upgrade. But like you, at least for now, a replacement is not truly a necessity. Decisions ...