Business investments will come back to the U.S. from China in proportion to how high the Chinese Yuan climbs against the Dollar. The sooner, the better, the higher, the better...for jobs, infrastructure, and long term investments here.
Delay the Yuan re-evaluation and you delay (or even lose) those business investments that are going to China in the meantime.
In the short-term, however, you are correct that the overall sum and status quo benefits the U.S.
China is spending $195+ Billion to make a $120+ Billion trade surplus...so America is financially better off by more than $75 Billion per year in accounts recievable.
However, you've got to then subtract the lost U.S. business investments that instead went to China (from the U.S. and other countries) to get a more clear overall picture. I'd have to look it up, but I'd guess offhand that China had $30+ Billion last year in foreign direct business investments into China.
Frankly, I'd rather have a more equitable and fair...overt economy rather than one that's being directly manipulated via currency manipulation, and the sooner the better. Oh yeah, there is also the Magic Dollar effect in play here. A Dollar paid to a U.S. employee will typically be spent in the U.S., where it will help pay the salary of another U.S. worker, who in turn spends her Dollar in the U.S. in a Magic Dollar virtuous cycle...but that wonderful leverage that we see via the Speed-of-Money disappears when the U.S. worker spends her Dollar on a foreign product. Poof! The leverage is gone. She got a cheap product and saved a few cents, but that Dollar is no longer in the domestic Magic Dollar cycle.
I'm just not excited about seeing a small net financial gain (whoo hoo currency traders! Lets all go work in the pits!) for the U.S. at the expense of losing our entire manufacturing base...especially when one considers that at some point in the future we'd be vulnerable to an OPEC style product embargo strategy from places like China.