There is nothing wrong with having your VSTi’s input set to ALL. Just make sure that you configure the ALL setting so it doesn’t include inputs used by an X-Touch or any other controller surface.
In general for the ALL MIDI setup you should include ports that have stuff attached like a MIDI Keyboard or Drum Pads, i.e. stuff you play music with. And it should exclude all the ports connected to stuff you use to control Cubase’s behavior.
Counter-intuitively ALL doesn’t really mean everything. 
Rather it means only those ports you decide to include.