Among libertarian investors, gold and silver related investments tend to be popular. It is because hardcore libertarians do not trust the Federal Reserve and the federal government. They understand that money can be created out of thin air and it is done on an almost continual basis for the benefit of the large banks and to enable the government to deficit-spend.
So what is the difference with platinum and would this also make a good investment? First, I think it is important to realize the differences between the metals. Gold and silver have a history of being used as money. Platinum does not. Platinum has uses as an industrial metal. Silver does too. Gold's uses are more limited outside of being used for jewelry and being used as a store of value/ investment.
Central banks do not buy platinum. Then again, central banks do not buy silver either, at least to my knowledge. So again, it all comes back to the fact that the market has chosen gold and silver over thousands of years as having good qualities for money.
I am an advocate of setting up a permanent portfolio, as described in Harry Browne's book Fail Safe Investing. I think that at least half of your portfolio should be in something similar. As a hedge against inflation, I am mostly a proponent of using gold and gold related investments. I think it is safe to have a small percentage in silver, but it should only be about 5%. Silver tends to be much more volatile than gold.
For speculative purposes, I see nothing wrong with owning a little bit of platinum, especially now. Although it is not a monetary metal, it will still have a certain correlation with other metals and with commodities in general. It will also benefit from a weak currency.
The price of platinum, in terms of U.S. dollars, was double that of gold a few years back. Now the spread is only about $230 as of this writing and that is with gold trading just above $1,500 per ounce. The gap between the two metals has narrowed significantly. It just shows that gold has gone up partially because of its monetary qualities.
With the ratio of platinum to gold going from about 2 to 1, to less than 1.2 to 1 in just a few years, it makes platinum an attractive buy. Platinum is not near all-time highs like gold right now.
So if you are looking for a speculation right now outside of your permanent portfolio, platinum might be a place to look. I don't know of any ETFs that invest solely in platinum like there are for gold and silver. You can easily buy platinum eagles from most reputable gold dealers. It is a speculative play that is another investment option for a falling dollar that is continually being devalued by the Fed. I would recommend that platinum be less than 5% of your total portfolio if you are going to pursue this strategy.