http://dollardaze.org/blog/?p=107
Eventually ALL paper currency goes to nothing. Like around the world, practically every country uses paper, backed by nothing. It's just the US prints money faster, so their value goes down, but all paper money has no real value.
But that's not to say you don't want to have any dollars. If you look at the stock market, you could play the paper money game, and invest it in stocks, and get more paper money, and use it to buy more real assets like houses and gold and food. If you just held gold in the last 25 years, it went up maybe like 3x, but stocks have gone up like 10x.
I would say diversify in a lot of things. You don't want to hold only one type of investment, cause the federal reserve could do what it did in the late 70s, and spike interest rates to lower inflation and increase the demand for dollars. It strengthened the dollar, made gold less attractive, and having dollars and putting them in CD's earning 20% interest a lot more attractive.
If your parents can, maybe consider buying some real estate and rent it out, that's a stable alternative. You have both hard assets (land) and monthly income (dollars). But yeah, diversify, don't put all your eggs in one basket. (for full disclosure, I personally have 1/3 gold, and 2/3 stocks).