Hi supermanx,
Based on your earlier posts when you first bought the mattress it seems like your mattress wasn’t a particularly good “match” for you from the beginning. I don’t know the specifics of your body type but it’s quite possible that the mattress may have been too soft for you in terms of support (even though I know that it may have “felt” too firm in terms of comfort/pressure relief) and there is always a risk if you purchase a mattress that is “on the edge” of being too soft for you because even a relatively small amount of foam softening can put you “over the edge” of the range of support/alignment that is suitable for you even though the same mattress may have many years of life left in it and would still be suitable for someone else for much longer (see post #2 here). Even the original Tempurpedic that you were replacing that was much firmer and lasted you for 7 years may have been suitable for someone else to sleep on for much longer (some people have slept well on the same mattress for a dozen years or more).
The overall softness of the mattress along with sleeping closer to the edge could also be a contributing factor to the edge support issues you are experiencing as well (see post #33 here).
There really isn’t any way to quantify the “value” of a mattress based on the amount or cost of the materials inside it and in some cases this can be more misleading than helpful. Post #13 here has more about what I would consider to be the most important parts of the “value” of a mattress purchase. I would keep in mind that the Tempurpedic you were happy with in the past was much firmer and had a thinner/firmer comfort layer (see here).
Phoenix