Hi qtonic,
I think that the value of both mattresses are roughly equivalent (which is typical of the same manufacturer which tends to have similar “value” across their entire lineup).
You can see some of my thoughts about the difference in the density of the base foam in post #14 here.
You can also read Dreamfoam’s comments about it in post #4 here.
The tradeoff in other words is that the 1.5 has better performance and for most people is not an issue in terms of durability because the top layers are the “weak link” in a mattress but for those who are in a heavier weight range and “go through” the top layer more then the 2.17 lb polyfoam may make more difference in terms of durability or for those where the better exchange policy or the better materials in the cover of the Bamboo Bliss (which includes wool in the quilting) are more important then the Bamboo Bliss may make the better choice.
Phoenix