Reading the above, I'm not sure if people are talking about the same vouchers - remember there are two types currently in circulation:
- The *A vouchers sent out earlier this year which are limited to specific fare classes and are good for (just about) any *A airline
- The BD *G vouchers which are issued on reaching or renewing Gold. These can be used with any fare,on BD only, except inclusive tours.
The downside about using upgrades on BD transatlantic from economy is that you only get into the New Economy, which, IMHO, is not much better that UA E+.