a vintage-film-look absolutely echoes the imperfection of vintage lenses.
i believe spektrafilm should be thought as a simulation of film, like thinking as if the digital sensor had the same limitations (and good qualities) of film.
lens blur simulation might be a bit out of scope here.
but indeed, there is already a control for lens blur that you can use to emulate the softness of the camera lens by blurring in the right stage of the pipeline.
and adding chromatic aberrations or simple models for astigmatism and coma could be interesting to try. maybe a bit out of scope again, but thank you for the suggestion!
the best vintage lens simulator might probably be just shooting with one (or a modern proxy for it, like my trusty voigtlander 40mm f1.4)
manual focus, only manual exposure and manual wb, vintage style lens with only manual aperture and only spherical lens elements, glimmer glass for additional softness and blooming. i think i am getting down the rabbit hole of analog simulation madness, and no one can save me.
pluuuus… a real time spektrafilm LUT and you get crazy vintage looking SOOCs
(still fine tuning the LUT stuff, stay tuned, coming soon)