One thing that does work, in Keyboard > Application Shortcuts set xfce4-popup-whiskermenu to Alt+F1 then your super key will still open Whisker but only on a quick release, it will not open if you hold it down which allows you to assign other shortcuts to it. See this thread for more information, there may be one additional step you have to take if it doesn’t immediately work for you.
I have whisker set to open on Ctrl+Space because that is what I got used to using when I was a Windows user and using Launchy. But I hear you, there should be a better way to set it to on release, and there has been a lot of discussion over it. It looks like there are a couple patches for libxfce4ui available that do set it to on release but I have not used them.
One thing that does work, in Keyboard > Application Shortcuts set xfce4-popup-whiskermenu to Alt+F1 then your super key will still open Whisker but only on a quick release, it will not open if you hold it down which allows you to assign other shortcuts to it. See this thread for more information, there may be one additional step you have to take if it doesn’t immediately work for you.
I have whisker set to open on Ctrl+Space because that is what I got used to using when I was a Windows user and using Launchy. But I hear you, there should be a better way to set it to on release, and there has been a lot of discussion over it. It looks like there are a couple patches for libxfce4ui available that do set it to on release but I have not used them.