Spotlight shortcut Cmd+Space stops working in Yosemite

Have you tried changing your Spotlight shortcuts? You can set the spotlight shortcuts (or any others) to whatever feels good for you.

Apple menu > System Preferences > Keyboard > Shortcuts > Spotlight

Click the shortcut you want to change, then tap the new shortcut keys on your keyboard.

A quicker way to launch commonly used applications would be to set a shortcut to launch a specific app. to do this, create an automator script to launch the application then set a shortcut to run the script. Here's a tutorial that explains how to do it. https://computers.tutsplus.com/tutorials/how-to-launch-any-app-with-a-keyboard-shortcut--mac-31463

Delete the spotlight preferences file:

~/Library/Preferences/com.apple.Spotlight.plist

And then reboot. I was having the same problem and that fixed it for me.