  This paper is the last in a series, investigating the optical properties of a
sample of mid-IR Warm Seyfert galaxies and of a control sample of mid-IR cold
galaxies. In the present paper we parametrize the morphologies and interaction
properties of the host galaxies and combine these with the major conclusions in
our previous papers. Our results confirm that nuclear activity is linked to
galactic interactions. We suggest an alternative view for the simple
orientation-obscuration model postulated for Seyfert types 1 and 2, that takes
into account the time evolution of their environmental and morphological
properties. Within this view, an evolutionary link between starburst-dominated
and AGN-dominated IR emission is also suggested, to account for the
observational discriminator (mid-IR excess) between our Warm and Cold samples.
