Quote: 1. Lenses which perform at their "true" focal length.
There is no "true focal length". Only the focal length for which the lens is designed... APS_c K mount can use both APS_c and FF lenses at full resolution... an FF can not.
Quote: 2. Larger prints at higher resolutions.
if and only if, for some reason, 24 MP is not enough for you.
Quote: 3. More dramatic DOF.
An advantage when shooting lenses wide open, stop down one stop and you can do on one what you can do on the other. While FF gives you more narrow DoF possibilities, APS-c gives you more wide DoF possibilities. Which is more dramatic? It's a trade-off. Not the same but pretty much equal.
Quote: 4. Having the cachet of a professional.
Shooting FF doesn't give you the cachet of a professional. Being a professional gives you the cachet of a professional. I know lots of guys shooting FF that have the cachet of a point and shoot shooter.