I was able to eliminate my wifi interference issue (when I was using the wifi Roku remote that comes with Roku Ultra+, it was disrupting other wifi signals in my house) by switching to a IR-only remote [purchased on Amazon]. Using the IR-only remote still fully controls the Roku Ultra+, but I don't have the wifi interference.
I did not change any Roku settings.
I use an IR logitech remote. Before i just gave up and wrapped in faraday fabric, the wifi signal on the rokus used to cycle in strength as if they were broadcasting for a wifi direct device on a interval. I was able to 'temporarily fix' this by doing what you suggested, and turn off all the wireless features I could from the settings menus. However this would get reset on reboots, upgrades, etc....so it was quite annoying.
Now i just stopped having to tinker with it by wrapping in faraday fabric and hoping the CPU doesn't overheat. So far its been good - with a few warnings here and there. If I had a backup roku device, I would crack them open and attempt to remove the radios...but the faraday fabric is doing a good enough job.
