It's still the love of knowledge to this day.
> Now that sciences and technology rule the knowledge field, philosophy's enthusiasts just claim that philosophy helps learning to think and widens one's spirit.
Science ( aka natural philosophy ), is just a small part of what we call knowledge.
> If that were true, I think philosophy would be a mandatory study to anyone interested in advanced scientific theories,
Science is a part of philosophy. When you get a PhD in physics for example, you get a doctorate in philosophy. It's just philosophy confined to the study of the natural world guided by empiricism. Certainly most scientists have studied some philosophy.
> Even so, most arts can claim the same: "grasp new ideas" and "open to fields of knowledge". In my case, I could say that for literature.
We can say philosophy is an art form centered around reason. Using the broader definition of art, everything is an art.