I agree with much of your post, except this part. There is nothing about running trade surpluses that should affect a country's currency; a trade surplus merely allows a country to amass foreign currencies, which don't do much. China's currency should be super valuable, right? But it's still cheap to buy Chinese stuff.
It is true that trade deficits should (theoretically) lower the value of your currency on the world market, because more of your currency is out there, looking for something to buy and/or being traded for other currencies, but I don't see a lot of this effect, either. Things are pretty stable, even though most countries run their trade surpluses or deficits pretty regularly. There is only so much you can do with a pile of foreign currency, really, and if it isn't used to buy goods denominated in that currency, it is ultimately saved (in the form of bonds) by *somebody.* That's why countries own lots of U.S. debt. It would be great if they spent that on American goods, but that doesn't always align with their economic goals. China would much rather just produce stuff themselves, if they are able, and grow their own economy.