You are quite astute to realize that wealth is one of the prominent themes in Robinson Crusoe. It's not one that students often pick up on right away. Crusoe's attitude DOES change in the story and, yet, the novel does end with Crusoe having money as a merchant once again.
First, it's important to note that money does have quite a bit of value at the beginning of the novel (it is only after Crusoe lands on the island that the value of money changes). The character of Crusoe shows the amount of money he has obtained, how he uses that money, and what the result is (i.e. success). Crusoe is so used to using money as a way to determine the worth of a human being that he is thrown for a loop on the island. Suddenly there is no use for nor value for money of any kind. Survival is key. As Crusoe becomes more and more successful at survival on the island, he begins to salvage items from wrecked ships. At one point, Crusoe comes upon a vast amount of money and simply cries about it.
I smil'd to my self at the sight of this money, O drug! said I aloud, what art thou good for? Thou art not worth to me, no not the taking off of the ground, one of those knives is worth all this heap, I have no manner of use for thee, e'en remain where thou art, and go to the bottom as a creature whose life is not worth saving. However, upon second thoughts, I took it away.
Note this is a statement spoken by Crusoe, not a question. Money is now good for NOTHING. A bit of rope, a small morsel of unspoiled food, a knife, etc. are all worth more than money. It is whether something is useful that denotes its worth on the island. A knife "is worth all this heap."
However, it's important to note that money is still a treasured item for Crusoe (even on the island). Why? Even though usefulness determines value on the island, money is a nostalgic reminder of civilization and the life that Crusoe has left behind. Despite the exciting adventures on the island, Crusoe does wish to return to England.
Further, upon returning to England, Crusoe begins to value money once again, as that is the mark of value in English society. This measure of success is the only way for Crusoe to establish a connection yet again with the society that he left behind while he was on the island. The facts of the novel prove this. Crusoe sells his land and home in order to settle down with the nephews he loves. Why does he sell his land and home? He needs the MONEY from the sale of that plantation in order to live comfortably. Crusoe ends up marrying and having children. It is only after the death of his wife that Crusoe returns to the island, finds the mutineers dead and gone, offers supplies, and then visits Brazil.
Thus, the attitude toward money in Robinson Crusoe is based upon what truly has worth. On the island, money has no worth whatsoever; therefore, Crusoe learns to devalue the money that, as a merchant, was always so important. However, once Crusoe returns to the civilized world, money regains its value once again as Crusoe must survive as a businessman.