In a discussion with a friend, the idea that a significantly decreased speed of light would make objects appear more distant (the light takes longer to travel to the observer) was presented. I'm not so sure about this, I think objects would appear the same size and shape because they're coming from the same direction as before, only redshifted due to the loss in energy. We also thought about if light experiencing more curvature than before due to being within the gravitational field of large celestial bodies would make them appear in different locations relative to where we currently observe them. Also, perhaps everything would appear a little dimmer, as the light is hitting our eyes with less energy.
In a theoretical alternate reality where the speed of light is half of our measured $c$, and that other constants depending on $c$ have changed proportionally, what visual differences might a human observer from our present reality see, and why? Are the ideas presented above realistic at all or way off? Please note that I'm not interested in a discussion on the validity of the theory above, only what theoretical effects a slower speed of light may have on optics.
If possible, I would greatly appreciate being pointed to resources with formulas for calculating these effects - I have some interest in writing a renderer capable of simulating them.