I think it's fair to say that anyone able/willing to pay the full $6k or $7k up front is better off doing that, with zero risk of missing out and immediate seat selection (for that coveted window seat). The airport upgrade or the bid upgrade seems cheaper than buying the mixed class fare for those who want to upgrade just the 14hr leg, but again it's a gamble.
I like the flexibility that the upgrade option gives you, especially if you've already bought the economy fare a few months back, helps with the cash flow!
I'm hoping to upgade to business on the A380 in March between AUH and LHR, although I realise this is the shorter leg, and in my opinion not good value, I'm looking forward to seeing the A380 product and hoping it will be even better than on the A340 which I think is the best I've ever experienced.