It might be different for different computers but I could not get the setting you tried to keep temps low on my computer either. I could however disable-turbo-mode and that lowered the temperature to a reasonable amount. Helped with fan noise too. My system is an amd 4000 thinkpad.
I get invalid for every single CPU. This is especially a problem for systems that naturally run hotter and do not have a lot internal cooling. The Qubes developers should look into this. I think this is likely affecting more users than just me and may also be making it harder to run qubes for some new users.
Can I take a graphical fedora program like cpufreq-gui and just copy it into dom0 using cat and then run it?