Originally Posted by
David-A
Erm, if you pay cash to upgrade, you will be in a cash fare code in the higher cabin. AA should give you exactly the same earning as someone who bought a cash fare in the higher cabin originally.
[They should see no difference.]
I can only make a guess as to exactly what OP meant, but mention of "bonus
status miles" makes me perhaps think the OP refers to the added Tier Points in BAEC on a CW vs. a WTP booking.
American uses Elite Status Miles and Elite Status Points, both of which are calculated as a multiple of flight distance, and multiple never exceeds 150% (which for a BA itinerary would apply for all the following FA JCDRI WET YB), so it's quite correct to say that AAdvantage doesn't give you a "status earning" advantage for moving from WTP to CW, whereas BAEC certainly does.
FWIW I used to maintain status in both programs. I now only bother with BAEC, as it's easier for me to reach status using the paid premium fares I tend to buy, and the status is more useful as it gets me lounge access on AA flights where no CoS will permit lounge entry on its own (North American flights).
As for using miles, utility of one program over the other is very route dependent. On the whole, since Avios changes came into effect, AA is still better for longhaul (especially multi-flight) redemptions, whilst BA is better for short redemptions. YMMV of course.