Yes, WT+ to CW is a good deal, but a) it is very rarely available for my route (GCM/LHR), b) Caribbean members can't earn miles on discounted Y, plus we can't get US or UK based BA credit cards and we don't have Tesco
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Alternatively, AA offers miles on all classes of service, offers 100% mileage bonus if you fly 50k miles a year (no Tier Points required).
A typical off season discounted Y fare from MIA/LHR is about US$500, you earn about 20k miles on a rt (if Platinum or EXP), you can use 25k miles to upgrade only the overnight leg (AA gives you that one way option), you can choose (at time of reservation) one of the extra legroom seats in row 31 on the 777 that is the seat of choice on the daytime flight.
About 5k net miles cost (less if you use one of the frequent winter booking bonuses) and about $500 gets you upgrade to Business in AA.... yes, it is no Club World, but still my favourite deal.
Oh, and Caribbean members of AAdvantage can get the Scotiabank MC which is 1 mile per US$.
That's the competition for BA upgrades, at least for the Caribbean.