Let me put it to you like this:
US Airways probably has the best TA business class, in terms of service, comfort and individual personal entertainment centers on the Airbus 330's. They are some of the newest craft in service, and it shows.
You can upgrade from a coach fare to business for 10K miles one way.
Using their triple miles promotion you will almost certainly earn well over 10K miles on the overwater leg.
Therefore you have not only upgraded for free, you've actually earned a couple thousand miles to boot.
Can you really think of a reason NOT to upgrade in this scenario?
Regards,
-Bouncer-