Hi StewD,
You can see a few comments about Cotton Cloud Futons in post #34 here and post #3 here. I don’t have any personal experience with their futons but they have certainly been knowledgeable and helpful when I’ve talked with them.
Both the comfort and durability of a futon, just like a mattress, will depend on the specifics of the materials that are used inside it so it would depend on how the specific layers and materials inside your futon compared with the new one that you choose. Higher quality materials will last longer and outside of the wellspring fiber they may be using different materials in their current futons. You can see a little more about the materials they used to use here although they don’t specify the quality/density of either the E-Foam (which is probably HD polyfoam) or the Ultrafoam (which is a higher grade called HR polyfoam). There is some information here about two of the futons they used to make and perhaps Cotton Cloud would know what was in the model you have and have a current model that is similar in terms of comfort and the quality of the materials.
Re-layering your futon would be similar to rebuilding a mattress and whether it’s worth it or not would depend on what was inside your futon and the condition of the materials. I would suspect that after 16 years that the foam and fiber in your futon would be at the end of their useful life and there may be little that can be re-used and you may be better off buying a new futon but it would certainly be worth calling them to discuss it.
Phoenix