I don't know what you mean by "pegged". 

To a first approximation, if the dollar lost 90% of its value tomorrow, the US would not become significantly poorer.  Everybody woudl still own the same homes and cars and tamagochis, the same bridges and roads would still be there,  barbers and doctors would still serve as many patients as before.  By hypothesis, all prices would go up 10 times, and thus all salaries and fees would have to do the same.  (In the countries with hyperinflation, most people manageto survive somehow).

Such a massive devaluation would have plenty of secondary bad effects, for sure.  There would be all sorts of financial disasters due to contracts with fixed payments in the future, dollars held by or owed to foreign parties, etc.. People would need to carry and use a lot more banknotes when paying in cash.  The devaluation presumably would be due to massive emission of new currency by the government, which would result in wealth being taken from citizens, as a form of global tax on money holdings and unindexed credits.  It is these secondary effects that make high inflation and hyperinflation so bad.

But it is precisely because of the possibility of inflation, money printing, and wild excursions in currency exchange rates that one should ignore the money when evaluating a nation's wealth, and focus only on actual things and services.

Of course, central banks and economists who are interested in the money itself, rather than real wealth, will have a different approach.