A return to the gold standard would be a move in the right direction as it would allow currencies to be backed by an actual asset and would not allow governments to manipulate and irresponsibly spend money to ultimately ruin currencies.
However, I am of the mindset that competing private currencies would be a more effective route. This would allow the best, most efficient currency to emerge.
See the following Mises article for a little more detail on the Gold Standard:
http://mises.org/story/3368
A search on the Mises site will reveal more about gold as a currency.
The following link to Rothbard's Man, Economy, and State chapter on money will offer you additional information about the concept of money:
http://mises.org/rothbard/mes/chap11a.asp
There are probably a few different ways, or a combination of a few ways, to answer the question about which country is the wealthiest depending on if you are evaluating based on government wealth, personal wealth, or a combination. Here are some potential measures:
1. Per capita GDP
2. Per capita GNP
3. Per capita personal income
4. The level of personal and national debt
5. Savings levels
