Those tiaras could be broken up and sold, if they are lying vaults, and no one uses them.
As we have seen this last year the Halo Scroll Tiara more than meets your criteria for being broken up and sold off.
"The veil is held in place by a Cartier ‘halo’ tiara,
lent to Miss Middleton by The Queen.
- The ‘halo’ tiara was made by Cartier in 1936 and was purchased by The Duke of York (later King George VI) for his Duchess (later Queen Elizabeth The Queen Mother) three weeks before he succeeded his brother as King.
- The tiara was presented to Princess Elizabeth (now The Queen) by her mother on the occasion of her 18th birthday."
The last time it was seen/worn in public was in the early 1970's.
As we know from HM's gifts to her her daughter's-in-law, Diana and the Lover's Knot and Camilla and the Delhi Durbar and later the Bucheron, and now her granddaughter-in-law Katherine's Halo Scroll, that "loan" is, for all intents and purposes a "gift", albeit a gift with strings, in that it is supposed to stay in the main line of the BRF and, eventually revolve in and out of the vaults.
The funds from that could be used to build hospitals, help unemployed workers, any number of things. Build homes for the homeless. Yes, it would be a finite amount, but it would help.
A drop in the ocean but following your logic whatever tiara Katherine wore for her wedding, it would not have been the Halo Scroll as it would be
"history", with a very small
"h".
I am not suggesting that the ones that she wears be used. But wealth lying in dust, when people are in need is unnecessary. The "scam" of sovereign to sovereign, is that not only are taxes from those who can afford it the most not collected,
That's big of you to allow her to retain those she "wears" but let's face it, the Sovereign's personal wealth is mostly in assets, property such as her jewellery and wouldn't the sale of them, less tax, fetch a magnificent amount paid by someone with access to the best tax Accountants and Lawyers that their billions can buy, and you can bet the government wouldn't get any tax out of them!
. . . but the queen "loans" out to non-sovereign relatives the bounty of this tax free acquisition. Camilla has the Queen Mother's ring, the Bucheron Tiara, etc.
The Sovereign to Sovereign transfer is enthroned in law to preserve the history and wealth of the Sovereign. Whilst Camilla is not a Sovereign, she
is Royal. The wife of the Heir to to Throne. Camilla's style and title in full:
Her Royal Highness The Princess Charles Philip Arthur George, Princess of Wales & Countess of Chester, Duchess of Cornwall, Duchess of Rothesay, Countess of Carrick, Baroness of Renfrew, Lady of the Isles, Princess of Scotland. As such she represents
"The Crown" at various State Dinners, etc. and if the Queen had sold off the contents of the Vaults, she would not have anything to wear, as indeed would her granddaughter-in-law, Katherine, who is now "entrusted" with the Halo Scroll which, if we are very lucky, we may see in action during the Diamond Jubilee.
Joe worker may inherit some bits and pieces from his father, but he is taxed and if he can't pay the tax he must divest himself of the "goodies".
And if HM decides to sell hers she too must pay tax on the sale. On the other hand, if each generation of the monarchy sold off that jewellery not in current use, not only would they have to pay tax on the sale, they would then need to buy new jewellery every generation to cover the BRF on State Occasions.
The whole deal would be an exercise in diminishing returns however, as since they had to give away the profits from the previous sales, not only would they would not actually be able to afford to buy replacements, but within a short space of time they would be personally broke!
However, should HM start selling off such treasures as the Delhi Durbar, etc. I am sure the Government would end up in a bidding war on the open market in an attempt to retain what they would see as pieces of
"Their History". If you actually believe that this is good for the Monarchy or the country and of positive economic value of that little exercise, you are the President of Fantasy Land!
It is obvious that you miss the point of the Monarchy as a whole and the position of Her Majesty in particular. Among other things she holds the contents of the "Vaults" in trust for the BRF for the use of future generations when carrying out their royal duties, as in the case of the Delhi Durbar Tiara, created for an especially significant historical event of international importance.
The Jewellery of HM is an historical treasure that you would have her dispose of as it is greedy for her to keep. Obviously your anti-monarchy sentiments blind you to the innate unfairness of what you advocate in that the Monarch has to give away her wealth but national and international billionaires and millionaires are allowed to accumulate as much wealth and jewelley as they wish. I think the Bolsheviks had much the same sort of ideals.
I would therefore suggest, that you apply your passionate Republican tendencies to the disposal of the cultural treasures of your own country and leave us to appreciate the
rich cultural and historical treasures of our Monarchy.
Oh and by the way, not only does the Queen has every right to gift her mother's ring to her son to give to his future wife as an engagement ring, whatever else lies in those vaults, you can bet your calculating little booties,
it is not covered in dust!
(Any historians here who know more?) I also sometimes wear artificial gemstones -especially for everyday life- but no fake pearls because it is so obvious if they are fake *lol* 
