Elon Musk promised a "wild" future full of advanced machinery.Tesla (TSLA 4.18%) was Wednesday's winner among S&P 500 index gainers, capturing the title with a more than 4% increase to its stock price on the day. There was little news of note driving the stock forward; rather, it seemed that bargain hunting and a somewhat cryptic tweet from CEO Elon Musk propelled it higher.A maturing marketWhile it's fine to be a leading company in an industry when times are frothy, the downside is that such a business can ...