As stated in my username I am a lover of Superman and Wonder Woman. Their friendship drew me in. They had such a sweet, loving, pure, and honest connection that was incredibly compelling. Kingdom Come solidified me as a fan. There's just something about two characters who are compassionate, noble, self-sacrificing, caring, and always looks out for the best interest of others before themselves that is evocative. When said characters are best-friends with underlying romantic tension it just takes it to another level.
What I loved about Superman and Wonder Woman in the post crisis pre-flashpoint era, was that in addition to their friendship, they had a beautiful bond that was incredibly strong and special. They were able to completely be themselves with each other in a way that they weren't with anyone else. They were able to be vulnerable with one another without fear of judgment. They were each other's confidant and voice of reason. They challenged one another, comforted one another, and supported one another. They had the foundation of what made strong, true lasting romantic relationships.
With all that is dark and wrong in this world, Superman and Wonder Woman were a source of light and goodness. They always brought out the best in each other despite recent and current narratives that try to say otherwise. This pairing is one that is powerful because it doesn't give into the pop culture trope. Instead it defies it by having the man and woman standing both literally and figuratively on equal ground. Their relationship is one of balance. One doesn't get propped up over the other to show how interesting or capable they are. Also, despite having many ideals that connects them they also, at the same time, have fundamental differences which challenges the other and only serves to make their relationship interesting.
I believe that the pairing of Superman and Wonder Woman serves as a counterpoint to the superficial thinking that the only interesting relationship is one that is either filled with angst between the two characters, or that the two characters must be polar opposites for the story to be interesting. SMWW provides a more nuanced story because it challenges classical tropes of gods and mortals. It actually allows readers to see the humanity of these characters who are viewed as gods but who in actuality are very human, if not more so. Because there is no defaulting to the human love interest being the reason for their humanity, you get to see the humanity in Diana and in Clark/Kal due to who they are and their upbringing. It is seen in their morality, their compassion, their love, their fears, hopes, loss, joy, pain, aspirations, etc. All these things which define humanity. It is not about being "grounded," but in how well one can connect and care about others. Those are what defines humanity and is what humans themselves seem to struggle with.
I always felt that DC did a great disservice to Diana by not having her end up with Clark/Kal during the post crisis era. He was the one man she trusted and loved above all else, and they deserved to have their chance.
In my head canon, post crisis/pre-flashpoint Wonder Woman and Superman are living their happily ever after in their own universe.