Originally Posted by
Apieinthesky
An award upgrade using AA miles on BA metal, first requires a full fare ticket. BA's WT+ isn't really the equivalent of AA MCE. BA considers WT+ a separate cabin, so an award upgrade from BA WT only gets you into WT+.
I believe you can upgrade from a at least B as well as Y fares. Depending on the OP's plans (and who's paying?) it may be worth checking the rules.
As you say, WT+ or Premium Economy on most of the European carriers gets you noticeably more space than MCE. MCE is the current / out-going 9-wide coach seat with more leg room. The PE products have one less seat across the cabin and at least a 38" pitch plus a leg/foot rest. Overall I don't feel like I'm continually brushing shoulders with the next guy and can open my PC in reasonable comfort in PE seats which is not the case for me in old coach, let alone the super, new 10-wide version.
The OP didn't say where his Wife was traveling from, but is AA/BA the best choice? A direct flight + car or even train might win over a connection.