The most important thing to remember is that Walt Disney envisioned a place where parents and children could enjoy the park together.
The Haunted Mansion is specifically built to be a family ride. It is a ride in which parents can be a part of their child's accomplishment of facing their fears of a haunted ride and being brave enough to make it through and realizing how fun it can be!
I am sure that those families that go to the Disney parks multiple times cherish how precious and fast time goes by as they watch their child avoid any possibility of riding HM, to thinking about riding HM, by being proud that they rode HM! And as Disney legacy goes forward, that child then gets to be in the parent role and watch their own child experience the HM and it reminds them of their childhood.
The constant flow of guests through the HM each day shows that guests love the HM. Could they use their Imagineer talents to modernize some of the special effects, sure. Just like they have done with the ending scene and the hitchiking ghosts. But all in all, it is not only a wonderful ride, a chance for a Magical famly memory - but a wonderful example of Disney history.