The SMC Takumar normal lenses that came with the Spotmatic-F are
unsurpassed.  I am not familiar with the Yashica equivalent, but I did
compare Takumars with Mamiya-Sekor lenses of the same period, and the SMC
Takumars had more saturated colors, deeper contrast and much less flare.
The difference was striking.

One drawback with the Spotmatic-F camera is that the meter comes on
automatically when you remove the lens cap, unlike previous Spotmatic
models, that had the meter switch combined with the depth-of-field switch.
I happen to use lens shades a lot, and it is a pain in the butt to have to
take the lens shade off between shots, so I can put on the lens cap.  I tend
to use my older body, a Spotmatic IIa, rather than my Spotmatic F when
shooting outdoors and using lens caps.  This may or may not be important to
you, depending on your shooting habits.  I personally have never liked that
feature.

The 55mm f/1.8, which was a cheaper lens than the 50mm f/1.4, will give you
sharper performance and better color saturation, along with less flare.  It
has one fewer element than the more expensive normal lens, and that
translates into less air-to-glass surfaces.

One other obscure fact: the 50mm f/1.4 lens used Thorium rare earth
component in the optical glass on the rear element.  Over time, the atomic
particles have broken down and the lens typically exhibits a darkish-yellow
cast.  Aside from having undesirable color shifting effects, it also means
that the 1.4 lens may transmit less light than even the f/1.8 lens does.
So, think twice before buying the purportedly "better" f/1.4 lens over the
f/1.8 cheaper one.  The 1.8 does not have any yellowing, and the optical
design is a tad sharper than the 1.4.  Sometimes the most expensive is not
necessarily the better choice.

I have heard that the yellow may be bleached out by exposing the lens to
sunlight or ultraviolet light for several days, but I have not tried it.  I
have three of those lenses, and I'll get around to the process one of these
years.