Thanks - those posts are very useful. You stop paying attention for a couple of months, and everything changes!
The Head for Points post, goes through the numbers usefully, but misses something quite important - that you still earn miles on the original class booked, when upgrading. So, for example, a PE to UC is now 20,000 each way on the LON to NYC route, rather than the 10,000 it was before (that was sweet!) - a doubling of miles cost, BUT... you still earn the PE miles and Tier Points for that original booking , and those miles are doubled with bonus miles if you are AU. So the net cost of miles is not 40,000 but maybe as little as 20,000 if you are AU, plus the bonus of TP to keep your status. this means it's still worth it, yes at higher miles cost than before, but you can get H PE tickets a bit cheaper than S/W so it's not all bad.
The tough bit is finding UC miles availability on the flight/dates you want, when you're not super flexible, or... rolling the dice and hoping that they open up in the future. I've won and lost in that lottery before now!