Thanks to all for your replies!
After chilling for a few hours I do realise that my post is a candidate to appear in the next AFF newsletter as "Self-entitled member really puts the W in WP".
In reality Qantas' decision here doesn't have too much real world bearing. I won't lose any lounge access privileges except for the AA Flagship Lounge when I transit LAX on domestic flights, being in the F cabin for AA Domestic still gives priority boarding and I travel with carry-on so there's no luggage allowance issue as a result of the drop to OW Sapphire.
By the same token, that's what annoys me the most. Aside from the risk that I cancel my booked flights after extending my WP membership Qantas has pretty much nothing to gain from rejecting my request. It's going to cost them the same in glasses of Veuve at the F Lounge regardless of whether I'm WP or SG at the time.
By rejecting my extension request all they've done is make me feel worthless - all these years and lots of money spent and they don't feel there's any need to reward that loyalty in kind, even in such a trivial way.
I just sit here thinking of one particular client of mine who spent 6 figures with me each year for several years, but hasn't given me much work recently. If he walks in the door tomorrow, booked in some more work and then asks me for a favour, do I tell him to get stuffed until the end of the year when the bills are paid and he's a 6 figure customer again?
A few people here on AFF reach QF LTG then take the opportunity to jump ship to BA (who have lifetime Platinum) or AA who have attractive points levels & low taxes for award flights. Trippin_the_rift would be the best person to ask in that regard.
Thanks - I'll send him a PM shortly and have a chat.