Google defines an investment as "A thing that is worth buying because it may be profitable or useful in the future."
I really dont see a way to say purchasing PMs is not an investment. How do you define the difference between hedge and investment? People invest in different things as hedges against various other things. Just because something does not pay a dividend does not mean it is not an investment.
PM stocks are more of a gamble in my opinion. Physical metal is not going away. but companies can go away. strikes, nationalization, poor management. Just look at the current situation, mines are going out of business because gold has fallen below the marginal cost of production. if you own physical metal you are fine, you have some paper losses if you bought in the last two years but that is all. If you are in mining stocks you could lose everything.
Those who bought physical gold in 2007 are sitting on large gains even despite the price drop. Many gold stocks are down 50% from 2007 levels. In the past you likely always come out ahead with physical. What happens in the future is anyones guess. perhaps the stock market holds together. perhaps people who time pm stocks become fabulously wealthy? or perhaps all digital based computer traded assets become worthless. perhaps governments nationalize brokerage accounts or raise capital gains to 60%? Most mining companies have majority ownership by large commercial banks so look out.
My advice: dont get sucked into get rich easy mentality. dont invest any more in any equities than you would comfortably care to lose.