Hi yirmiyahu,
The new Serenity Latex has a different “feel” and design from the old Latex Supreme and for lack of a better word the new one feels firmer or more “substantial” (that’s how it was described to me). The old one was fairly soft compared to many other latex choices.
Both of them have no weak links in the mattress so from a durability point of view both would be good choices (2.5 lb polyfoam is a high quality material and the comfort layers are the most significant factor in the durability of a mattress).
In terms of material value … the old one had 9" of latex (3" of it was convoluted on each side) and was $1559 in queen (mattress only) and the new Serenity has 6" of latex (3" on each side) and a core of high quality polyfoam and is $1449 in a queen so they are very close although in terms of “raw material value” I would probably give the slight edge to the old Latex Supreme but the new one may be a design that more people would prefer. With the new Serenity you are also sleeping more directly on the latex which would be more contouring because the Latex Supreme had 1.5" of polyfoam in the quilting of the mattress. The cover of the Serenity is also a good quality stretch knit vs the Damask (less stretchy) in the Latex Supreme
The raw material cost of a mattress though is only part of the “value” of a mattress and the differences are small enough that I would choose the one that was the best match for you in terms of PPP and your “personal value equation” because both of them are good quality/value choices and the one that “sleeps” the best for you would be the better choice IMO.
Phoenix