I am not convinced by those posts. For example if your investment is devalued by 20% due to the currency going down then the return will also go down 20%.
But once the currency has dropped, there's no change to investment. The only way it would bar investment is if there's a looming, unrealized drop, and the dollar is being propped up.
For instance, does it matter if it is $0.8 to 1 Euro or 1:1 in terms of investment? No. It does not. The only way it would bar investment is if it's 1:1 and investors are scared it will drop to 0.8:1.
Try it. Do the math. 0.8:1 vs. 1:1, you have 5 euros to invest, 10% return on investment, which gets you more money?
Having foreign debt marked out in US$ may not save the USA. It means that investors could refuse to loan the USA more money if they think the value of that money may go down in the future.
Protip: They might do that today. Any currency may, in fact, decline in the future.
If there are local substitutes then why are you not buying them now? Example oil. The USA does produce a little, but it imports most of its needs. If the value of the USA dollar goes down the USA has several choices, pay more per barrel, persuade the sellers to accept less per barrel (as the price is in $us this is the default, but the sellers could increase the price and sell to other countries) or buy less. It would have extreme problems trying to increase local production.
*shrug* - it's just going to fuel investment in alternative energy. New industries will form, over here, due to the increased costs.
New alternative energy and energy efficiency industries would arise to decrease oil costs, and new methods of doing so would become cost effective. That would create jobs. Overall, good for the economy (unless you're rich).