I wouldn't say translation of poetry makes you a better creator of non-translated material. In fact, in many ways, it actually makes you worse at it. Too much translation without creative language work of other kinds can ossify you, get you too much in the routine of working from template, of thinking in terms of the extraneous. Get you too accustomed to limiting yourself to the inventive side of creativity, to knowing exactly what you want to say before you figure out exactly how to say it. Most of the best translators of poetry are at best okay at writing it.