My wife actually pushes on me the other way.
I keep equipment for a long time and only upgrade when it's a BIG upgrade. I have a 20D and a 5D, and am finally looking to upgrade.
When I pointed out that I could get a 70D instead of a 7DII for a lot less, my wife asked why I would get something a little less good when I primarily use that camera for high-speed action and the 7DII is built for exactly that.
Okay, so she has a point.
The 5D replacement will be a 6D or a 5DIV, but not a 5DIII. The 6D is actually better suited than a 5DIII for my application for that camera, so we didn't have a disagreement there. But if the 5DIV is even better suited than the 6D, and it comes out in time, then she wants me to get that one instead. We'll see about that.
Your thoughts about the 6D vs the 5DIV are very similar to my thoughts a few years ago with regard to the 5DII. I intentionally bought a used 5D back in 2010 and waited until about a year after the 5D3 was released and bought it at a discount from the release price. I intentionally leapfrogged the 5DII. It sounds like you are thinking the same way about the 5DIII as I did about the 5DII.
And really, the 5D is a wonderful, beautiful camera. I love my 5D even if I don't use it much anymore. I used a 40D + 5D combo for several years with confidence and bliss.
OH... and I've taken thousands and thousands of images for many volunteer organizations, school, scouts, church, friends/family, etc. All for free because I love to do it. It feels like a job sometimes but it is appreciated so it's a win/win.