You can make something that looks identical with cheaper alternatives or even synthetic materials. Same with diamonds (see cubic zirconia).

Thus, it is not the actual properties that make them desirable as jewelry. It is solely the fact that they are valuable that people want them for jewelry.

hmm, perhaps, but historically you couldn't and so this combination of historical data, etc. as well as physical properties is what gives it value. But, yes, because of the issues you are talking about, going forward we should expect gold to be a bad investment, not a good investment.