Just to slightly hijack this thread, because it's triggered a lateral thought, if I switch from a free blue BA card to the paid BA card, having spent more than £10K, do I instantly get a 241 voucher from the new card? I've remember seeing something that suggests I do and I can see a use for that.
On the subject in hand, these loopholes come and go, I remember the glory days of stoozing where I offset my entire mortgage for 3 years with balance transfer deals, you could literally write yourself a cheque for thousands of pounds of interest free cash. Best not to recriminate, and look for the next one. My favourite of all was on a German betting site (bwin) which had a loyalty scheme. I figured out that by playing world football top trumps and raising the stakes to maximum when there was a no win/no lose bet, then playing for minimum stakes for everything else (essentially you would bob along without losing much), I could effectively generate infinite loyalty points which could be used for 400 euro a month cash, goods and merchandise (I got loads of shirts, poker sets, footballs, a PS2, etc) and raffle tickets (a friend of mine who was also in on it bought all the tickets for a VIP trip to Real Madrid, and of course won). It was truly the most gleeful loophole ever, and it took them three months to figure out what we were doing and shut it down. Even to this day the mention of Ronaldo (the original one) still triggers a slight endorphin rush.
In general, the life is being squeezed out of all loyalty schemes by the relentless march of cost reduction. Same will definitely be true of credit cards.