@ MickC
While I agree that gold has, over the long term, preserved its purchasing power even this requires that holding costs such as safe deposit fees be ignored. However, as mentioned in my earlier post, this is an argument for preferring gold to cash not a justification for holding gold as an investment in its own right – real estate, equities and bonds have all out performed gold by a very large margin in developed markets over the longer term (and often over the shorter term too). Further, many other asset classes produce a stream of income and, at the end of the day, we all have bills to pay. Investing in gold carries significant opportunity cost.
I'm afraid I am not convinced by your argument that the spreads on bullion are lower than for FX. Below are two links, one for HSBC's retail FX buy/sell rates and the other for BOCHK's precious metals buy/sell rates.
The spreads for 1 oz sealed maple leafs are over 4% which is, as you point out less than the spread on Thai bank notes. However, the bullion spread is wider than both the TT rates for all the major currencies listed and wider than the cash rates for several of them. And, of course, this is for a 1 oz coin which, depending on your needs, may be a rather inconvenient denomination and using half oz coins significantly increases the spread.
https://www.bochk.com/en/investment/rates/metal.html
https://www.hsbc.com.hk/investments/...exchange-rate/