The dollar is currently valuable because (most) everybody needs it to do their international business under the current central banking system, offsetting the fact that it is vastly over printed and devalued at the same time, its purchasing power has declined by 97.5% in the last 50 years against gold which is still the benchmark currency all currency's are compared against.

As crazy as it sounds the value and strength of the dollar is measured by it's annual continued creation of debt. If debt is continually being created and compounded by everyone then the dollar is viewed as strong and desirable.