"It hasn't impacted upon the value of the dollar." YET!
It is only trust and hegemony supporting the dollar. Neither have to last for ever. Russia, China, Iran for a start would love to use any currency but the dollar for world trade. Should that happen, the US dollar would likely take a hit to kick it clean into touch. Any currency has similar vulnerabilities when international trade is permanently in deficit.
As you state currencies float. This means they can also drown. Many are no longer backed by gold. If not backed by something tangible, what else supports them? Nearly 50 years on trust alone and Fort KNox merely a name-how much longer can the game continue?