But this is entirely subjective, isn't it? If you can prove that, say, gold density is equal to some figure (or pull out from your pocket a two thousand year old coin), but you can't impose the opinion that gold is nice looking on anyone because it is strictly for them to decide on that matter. They may not share this view and therefore gold will not have so much value on account of that, right?
Yes subjective. Both types of value is subjective. That is why everyone should decide what they want for themselves in the market, and what they are willing to sacrifice to achieve it. If you already have some of that what you want, that will change your values, also your total situation, and not least, your personal preferences. If you like fresh vegetables, you might want to trade some of your time in a job, to somebody who wants the work done, in stead of growing the vegetables yourself. Nobody has the knowledge, nor the right, to decide for others. This is why voluntary action is best: more freedom (by definition), and more wealth for everybody.
valuation of them? If you don't like the word "backed" used here, what is, in your opinion, the best term describing the sustenance of value by objective properties?