Keeping the higher power level weapon/armor piece is obvious. Yes, you will use the higher level one now. You may even infuse it into something now. The lower level one you should keep, as long as you have vault space, in the event that you someday get something that it can be infused into in order to raise its base level. I do so daily using weapons and gear that were seemingly worthless when I acquired them and which, like you, I sharded. And again, like you, I too deleted the lower lvl weapon/armor piece because at the time I failed to understand they may have value in the future. And it turned out they did.