The days of "having" to upgrade crop bodies is pretty much over. There's no reason to swap or sell a 7D for any other crop body....
Yes there is: much better ISO performance. I use mine for 'action photography' ie motorsports and wildlife and unfortunately find that I'm using iso 1600+ to get both the DOF and shutter speeds I want. Interestingly this is the body I would soonest replace. The 5D2 is miles ahead in image quality.
Every photog in this forum runs up against the limits of their equipment on a daily basis. One extra stop of IS, one more stop of low-light performance, etc. are useful adds to people who shoot weddings, indoor sports, etc.
I'm a 5D3 guy and honestly get frustrated that I need more than ISO 6400 for some shots (obviously, where a flash can't be used). Am I spoiled for being able to capture what we couldn't 20 years ago? Sure. But I still want to capture my human experience, and I often am in places and that are not ideal to shoot. Progress on every front with these rigs lets me net more keeper shots.
Applying this specifically to the 7D, the 7D2 having the 1DX/5D3 AF system alone
is worth the upgrade. That focusing system is world class.