For me, one of the most significant changes BA made to EC membership occured when members were no longer able to select seats (when booking or when checking in online) ahead of other travellers. In particular, this made it much more difficult for me to secure my favourite upper deck seats on 747 flights.
On the other hand, the recent promotion which allowed me to purchase Club World tickets to North American destinations for 50,000 Miles each (plus taxes, fees and charges, of course) was a valuable, albeit temporary, benefit.