I had some luck booking a package in one class and then calling to upgrade one way. Granted, I didn't know what I was doing at the time but still! I called during a sale and the adviser told me that a margin that is usually calculated and added on automatically wasn't being added and so I managed to book a WT to WT+ upgrade in one direction long haul for £83 each, when the difference between WT and WT+ booking flight only on the website was £381 each.
I also had luck a couple of days ago booking a fly drive long-haul from EDI- package price for WT+ return plus 14 days large car hire was was sub £1,900 for two whereas the WT+ flights from London only with no domestic connection and no car were over £2k. Was pleased to get my hire car and connecting flights for what seemed to be a reasonable price.