As your car is old, and producing so much problems for you, i can understand your feelings, iwill recmmend a kabuli/brand new coil, depend on your condition how you feel better for any, ANY can perform upto mark for you,
AS you said wiring is messy, LOOK wiring , coil, these things need replacement soon, you never know what can cause you, so do this pending work ASAP,
on sunday i was in suzuki 3s, i saw almost brand new cultus, i asked what happened, replied car caught fire due to a wire inside, all damaged from inside, THIS wasnt for you, but was a advice do wiring/coil work soon..
AS mentioned, wiring engine coil is in bad shape SO in context only a T-STAT valve will not do the work, iwill suggest you to do other work first instead on this,
BTW i didnt feel any thing wrong about temp, its an old car, and with ac on its only 30-35% hot, in my view its good..
that was my view, i might be wrong