I have both a 1D3 and a 7D2.
My recommendation would be to keep both if you can afford it. Camera-wise, the 7D2 is probably better, you get video, live view, a great LV AF, and you can go pretty high up on the ISO and get useable results. I don't think I even enabled the H setting on my 1D3 but found it to be useable up to 2000 or so, I have gotten fairly good results at 10,000 on the 7D2.
Noise wise, I think they're on par up to 800 or so, although the 1D3 might have a slight advantage, there's also the advantage that the 1D3 can have ISO50 enabled.
Ergonomics wise, the 1D3 wins by a long margin. I pulled it out today because we had a windchill somewhere near -10F and when wearing gloves I can't adjust the settings on the 7D bodies without accidentally hitting other buttons, whereas the 1D3 has just enough spacing on the buttons surrounding the ISO button near the top LCD that this isn't a big problem.
As far as rendering the camera obsolete, it depends on what you like to shoot. I actually bought mine used in 2013, after having a 7D for ~2.5 years and kept both, with the 7D being a backup, and only a primary camera if space was a concern, or I needed AF in live view, so while I technically bought a downgrade, the "better" camera became a secondary.
Right now I have been using my 7D2 a lot more, but as soon as the airshow season starts, the 1D3 will be my primary body for shooting static displays, keeping the 7D2 for action shots just because of the extra reach.
An important thing here is that this was a gift from your wife from back when the camera was new, so if you've only shot some 20k shots, the camera is barely broken in (the official shutter life expectancy is 300k), so you probably haven't gotten your (her) money's worth out of it. Another vote for "keep it".