I believe, and several politicians has said so openly that Alexandra got her apanage to maintain the living standard befitting of two royal children, who at the time were three and four in line for the throne. - After Frederik and Joachim.
There was after all a possibillity that M&F would not have children.
Another reason was to avoid a "Diana" at all costs. No bitter ex-wife speaking to the press all the time, so in a sense it was "behave-well-money".
But first and foremost I believe Alexandra got such a good bargain, because it was novel situation. There hadn't been a divorce in the DRF for some 150 years. And beforehand these sorts of situations were dealt with routinely by allocating the lady in question an estate somewhere in the countryside where she would retire and live descreetly and comfortably from the revenue. (I refer here mainly to women married to the "left hand", i.e. official mistresses).
And there were no official papers willing to print anything negative she might have to say back then.
The DRF learned after all from the affair, in the sense that Mary had to sign a considerable less advantageous prenup. And presumably so have our Marie.
(I can imagine a fuming newlywed Frederik grinding his teeth, but no doubt the prenup was very much "strongly advised" by the government).
Everything considered I believe it's money well spend. For some 25 million DKK, so far, the divorce has been most civillized, with very little bad PR for the DRF and as a consequence Denmark.
Joachim had to sell one of his golden eggs, Schackenborg Inn and probably realise some shares and what not in order to give Alexandra a reasonable sum, so the apanage was I imagine an additional incentive for her to accept less of what would otherwise have been 50 % of the estate. Which would propbably have meant that Joachim would have been forced to sell Schackenborg back in 2005 with a considerable less surplus if any.
There is no way Alexandra will be excempted from tax and vat now, that would be politically unacceptable for several reasons. The main reason being that only royals are excempted.
For a woman who is very aware of her public image it would be an obvious choice for her to request no longer getting an apanage once her children have left home. (i.e. no older than age twenty - or they ought to be kicked out
).
By then she can sell her current large home with a good profit and settle anywhere she should wish. She can also sit on any board she would wish, as she is no longer directly in charge of two members of the DRF, Nikolai and Felix.
She would still retain her high status, as holder of the Order of the Elephant and mother of two Princes.
And you would imagine she would have had time and the means to make enough sound investments for her to live comfortable for the rest of her life.
If she should not offer to give up the apanage in eight-ten years from now, the issue will flare up again, in earnest, and it will be difficult to justify her recieving such an amount. Politically it may be decided to cut the apanage by half or two-thirds and there would be very little opposition to do so. - Any "threat of going public" from Alexandra would by then be of little consequence and actually self-destructive. She would be seen as a "bitter old hag" should she do so. - And to be honest, I don't think she would do anything like that. The DRF and the state have in any way been very fair towards her.