The Amex travel credit was for Platinum cards I believe. I had a similar offer before when I had one which was a great deal but sadly they don't seem to do it on the BA Amex.

I guess the question is which do you value more Avios or cash? Obviously with Top cashback you can get Avios too but not much on £8.62! As madfish says if you add a car or hotel (even for 1 night and can be at the airport this end) then you would get more cashback but still only £30.52 with BA. You could get 4% with ebookers if you include a hotel night which makes the cashback £140=14560 avios but more hassle to upgrade.