You're absolutely right, but you're not buying the fund because you think the dollar is actually going to go to nothing. The US government would actually need to literally collapse, and the Constitution would have to no longer be in effect. It would be an apocalyptic scenario. Hell, I can come up with apocalyptic scenarios where the government stayed intact and the dollar with it. It would have to be real bad. BAD.
With that said, the very best Dow to gold ratios occurred in '32,'33,'74,'80, and 2011 which should resonate as REALLY bad years for stocks. If you're in a fund that's in precious metals you're not anywhere near those lows. At the same time, when business is good and stocks are cooking, you are still getting upside because you're not only in precious metals. You're in mining companies, too.
So what I'm saying is, you get the REALISTIC benefits of owning precious metals in a downturn, along with some of the benefits of owning stock in an upturn. If you really think that the economy will get so ridiculous that gold will be the currency of the world, then I can't help you.