One thing to keep in mind is that changes in currency exchange rates fluctuate and the dollar is unlikely to remain that low forever (what's your time horizon for investment?)
I'm considering investing in Berkshire Hathaway shares (brk.a and brk.b) right now (Essentially Warren Buffets enterprise). They invest in long term businesses and most of their investments are global so they're little affected by exchange rates.
There is also a number of global funds that you can invest in that are largely immune to that as well because the investment is spread across different countries i.e. currencies.
One of my favorite statements / advice from Warren Buffet is that he never invests in something he doesn't understand.
That means if you really understand how for example the gold market works, you might be able to make a lot of money speculating on that. You could also loose a lot of money if you don't.
The same goes for foreign currencies. You also need to be able to purchase and sell depending on the market which means that you need money at your disposal that you don't need otherwise. There's nothing worse than having to pull out of a bearish market because you need $20k to fix your roof only to see the market go up a year or two later.
As a long term investment historically the return on on gold has roughly been equal to inflation. It's probably the most secure form of investment but the return in real value over the long term is zero.