It's a very good question. I think it all boils down to personal consumption. For example, critics might comment on the high earn/burn rate. Which is true.

But I place value on the fact that I can upgrade any fare (ie saver or flex) and its easy to understand what is required. Also, from personal experience I have found upgrade inventory far more plentiful on EK than say, UA. QF is a joke.

As an example. This past Xmas, my family relocated from SIN to DEN. I found 2 x J one-way award seats from SIN-JFK. And I found an additional 2 upgrade awards. Meaning 4 J seats on 2 A380 flights. The cost of the Y tickets (which I upgraded with miles was approx $2500). Taxes on the full award seats was next to nothing.

Had I purchased those 4 one-way tickets - it would have cost me somewhere in the region of US$25,000

In this example, the value of the miles I had was huge. And I managed to find these seats 6-weeks out. In the middle of December.

I am the first to complain about the earn/burn rates, but I know that on the routes I fly, if I do use miles to upgrade, the product is consistent and when you factor in the chauffeur drive benefit, (could be valued at US$200 per trip, if you compared to a taxi charge), then I think the value is reasonable.

YMMV...