Actually, the performance might not be as bad as you would at first think. A good chunk of the work done by a graphical application is actually done by the graphics system supplied by the "OS", and in this case, that code would be natively compiled.
It's analogous (performance-wise) to writing gui apps in python - provided you're not trying to do any heavy lifting in the actual application code, it could work quite well.
Apple's Rosetta technology for running PowerPC code on Intel Macs actually worked this way, and the performance for most apps was really quite acceptable. That said, Rosetta had the advantage of moving from relatively slow CPUs to the fastest in the world. In the case of ARM / Android, you would be trying to run Windows apps on a slower CPU, so the results wouldn't be as good as Rosetta...
I agree with everything you have said. I would just add that I think many of the most useful (and widely used) Windows applications do do heavy lifting in native code — Word, Excel, and Photoshop are all good examples here. They aren't explicitly number-crunching like BTC mining or SETI@Home, but there is a lot of x86 code running under the hood.
It's analogous (performance-wise) to writing gui apps in python - provided you're not trying to do any heavy lifting in the actual application code, it could work quite well.
Apple's Rosetta technology for running PowerPC code on Intel Macs actually worked this way, and the performance for most apps was really quite acceptable. That said, Rosetta had the advantage of moving from relatively slow CPUs to the fastest in the world. In the case of ARM / Android, you would be trying to run Windows apps on a slower CPU, so the results wouldn't be as good as Rosetta...