Personal experience is the mother of creative expression. In that way, all fiction is a muted form of autobiography. The keen reader pierces the veil of fabrication and sees the heart underneath. It's frightening when you realize that writing fiction is a form of self-exposure. But a moment's reflection brings you face-to-face with the conclusion that that can't be helped. Vonnegut's experiences as an American soldier in WWII are an anchor in the storyline of Slaughterhouse Five. Steinbeck's experiences growing up in Salinas give generous contribution to the settings, images, characters and "feel" of his novels.
If the opening thesis of this post is correct, that all fiction is in some form or another a plagiarism of life, then a life rich in experience is an excellent (essential?) foundation for creating fiction. A theory is a theory is a theory; does empirical observation support this theory? Yes: Fitzgerald lived the excesses and indulgences of the Roaring 20s before he wrote his great American novel; Jack London watched more than one dog make a life in the Alaskan tundra before capturing their habits and lives in print; Melville was kidnapped and held on an island by cannibals while serving on the whaler, Acushnet, before he began writing of sea captains and whales and sailing; Vonnegut served in the infantry in WWII before creating his masterpieces about war; Camus lived in the hot sun of Algiers long before the final draft of his short and powerful novel, The Stranger...you get the point. If you want to write, get out and live.
I'm not suggesting that you spend the winter in a tundra, move to Algiers or get kidnapped by cannibals. What I am saying is that the time you spend living, working, loving and breathing is just as essential to writing as the time you spend sitting at your keyboard or couch stringing words together. The time you spend living, the experiential cache of your life, is what gives richness to your writing.
People-watch, gaze the sun set, listen to the ocean's song, follow the movement of animals, smell the autumn air, hear the bustle of stars on a dark winter night, fix your eyes on your lover's face while in the passions of lovemaking. It's all part of your life's experiences, all details in the glorious panorama of human existence, details that will breathe a third dimension into the characters and scenes of your writing. These details, when properly chosen and applied, will give your readers a memorable sense of experience when they read your work. A passionate life is the best source material for passionate writing.