I lucked out - just bought one today before the email arrived - soley to save the CC fees on a booking I had to make anyway, but should get the points. Looks like it is time to buy a few more.
The only possible catch - the card payment fee. The detailed T&Cs for the "old" vouchers issued before 12/12/12 specifically states no CC fee payable on the additional amount paid to make up the difference. the T&Cs for vouchers issued from today don't exclude the charging of the CC fee.
The "About" screen for buying the vouchers advertises "Qantas does not charge a card payment fee on gift voucher purchases or redemptions" which implies status quo, but refers to the full T&C for details - and does not seem to rule out a CC fee for paying any outstanding amount.
I am hoping that the status quo prevails (no CC fee). If not, then buying larger vouchers and rolling would avoid the fees until the "last" booking uses up the final value.
For what it is worth, I purchased a voucher ($50 by 2 people) this morning, waited until it finalised (for a while, it simply said "this voucher cannot be redeemed online), and then used it to book a return flight ($99 pp each way). I was not charged any CC fee on the remaining payment amount. If I had known about the new conditions (I didn't read carefully when buying the voucher, and am not sure that the website was even updated then), I would have put more money into the voucher - looks like I have missed out on 2,000 possible points.
