Next time you have this option, consider paying the fare difference to T and upgrading with Avios over the phone. A few weeks ago, I booked a discounted WT fare (Q bucket) and kept an eye on WT+ (T bucket) with ITA-Matrix. Last week, it dropped several hundred $, so I called BA, paid the fare difference to T and upgraded with Avios to J in one phonecall. This meant paying the change fee, but I considered the total cost (around $300 and 12,500 Avios) to upgrade worthwhile. At the time of booking, I had the option of 'pay just ca. $500 more for WT+'. I just looked and the fare difference is now ~$600 more, not including the change fee.

EDIT: Kevin, apparently I was typing this as you posted the above