You are right. At least for quite a while I will continue using my D300 at least in combination with the 70-300 VR - and probably, like your wife, carrying them both. One of our photoclub members also has a D800 - and regrets that he sold his D300, for specific uses. Old technology can have its niche benefits. Occasionally I 'even' still use the old D70 of my brother (as my old one fell to pieces) for IR photography.
But in general, sure, I will just use the D800, at full resolution. And buy as much memory as I can .