I tend to keep apps I'm not using closed. This happens a lot with Omnifocus. Unfortunately, that also means that I can't use the Quick Entry window.
So here's a macro that will open the app, minimise it (I don't hide it since the app loses focus and I can't use the menu afterwards), and then run the Show Quick Entry menu.
Let me know if you find it useful. I certainly do.
I know this is old, but wanted to put this edit out there for anyone who finds it and wants to use it. This macro still works if you take the last couple steps out of the conditional statement requiring OmniFocus to NOT be open. Took me a while but I got it to work in the latest version of Sierra and OmniFocus as of 12-19-2016.