In the end though, I think this whole debate is based upon Farplane = Lifestream (and possibly the brat Shinra mentioning the Farplane's energy)...
Farplane: Benign. People can visit. Full of pyreflies.
Pyreflies: A form of matter/energy that exists within everything. Found throughout Spira, but mostly found in the Farplane.
Lifestream (ok, my understanding of this is poor, but here goes): Bevevolant, ie, actively help to look after the planet. One body of energy/matter. Toxic/fatal to come into contact with
They are similar, materia condenses out of mako from the lifestream, and spheres condense out of pyreflies. They exist within everything.
Disregarding the death of enemies, they interact with the world differently. In X, Summons are only possible with Fayth, whose dreams are formed out of pyreflies, whereas in VII, Summons are just like any other materia. Though it can be argued that summon materia can be formed from the condensation of fayth pyreflies...