Depends who you ask. One school of thought is that gold plating gives you better contact connection as well as longevity without the worry of corrosion. Another school of thought is that gold plating can cause a slight diode effect which in theory can be detrimental to the sound quality.
Me, I personally don't care one way or the other. If the tube sounds better with or without it then that is what matters. I went from gold pin signal tube Mullards to non-gold pinned Pavanes and haven't looked back.