It was suggested to me that a useful technique was to sing with your eyes open, but pick a spot slightly above the heads of the audience so that looking directly at them doesn't become a distraction to the song - they are not looking at a 'closed' face - you are looking at the song.
Eye contact is fine in some types of song, but, in my opinion, never necessary unless you have no confidence in the song working (a sort of, "nudge, nudge - know what I mean")
We once asked Walter Pardon where he looked while he was singing - he replied; "At the microphone, if there is one - if there' isn't, down my nose"
He compared singing to reading a book _ "You've got to have imagination; there's no pont of singing a song if you can't see it".
He was a prodigious reader and had read all of Dickens and Hardy at least half a dozen times and could tell chunks from them all as detailed stories.
He once said, "it's a pity you can't read with your eyes closed" much easier to get into it".
Of all the singers we met, Walter was the most insistent that you had to become involved in the songs yourself to make them work.
Not sure that is possible if you are trying to catch the attention of a sea of faces.
Jim Carroll