It would kind of defeat the purpose of having a public open house to introduce people to Freemasonry (*wink, wink, nod, nod, recruiting tool) and say, "But if you think you might ever actually want to join, you can't come in." Our Grand Lodge building is on the main thoroughfare in Nashville and open daily for public tours. The George Washington Masonic Memorial is a collection of lodge rooms that are open to the public. Our annual officer installation is in the lodge room and open to the public; more than once we have received petitions from brothers/cousins/friends/etc. of new officers because they got a glimpse of Masonry.
Until the three great lights are displayed and the lodge is sealed, I see no reason not to show someone around. I even go as far as to open the door on the night of a guy's EA and say, "You are going to be blindfolded, but look, there are no holes in the floor and nothing you are going to step on. Relax, and listen to what is being said to you."