re: Epiphenomena yes but
I would consider it as having some meaning.
If we understand how the momentum of a photon is generated and why photons can interact with mass or how they obtain their velocity, then we would have advanced our comprehension of the universe.
It seem that there are several others searching for such answers, for instance G. Sardin has a very interesting explanation at this web site.
http://www.terra.es/personal/gsardin/vacu-doc.htm
