how many add an extra day of training to work weak points?

i'm talking at the end of the week, adding an extra day to hit muscles that have been well rested but still need to "catch up" or be worked more. been thinking about adding another day on friday to hit back and chest again, assuring that theyre 2-3 days rested. im thinking something like this:

monday: chest/tris
tuesday:back/bis
thursday: legs/shoulders
friday: chest/back

thanks for the response. one big reason why i dont do upper/lower splits is because im on the long road to a knee recovery and at this point, can handle training legs only once a week. as far as upper body, i seem to respond better to higher volume as opposed to high frequency, though this topics suggests otherwise :S

you know when you just finish a great workout, you feel fatigued and tight? Well I hate going into the weekend not having that feelings. That's why I was thinking about adding a final "touch up" day on friday to blast my body before the weekend. i know that sounds stupid.

I am naturally very long and thin so doing an upper/lower split (which I have done) feels like too little jam spread over too much bread. And then I start dropping weight, even if I eat alot. I have made my most size gains training high in volume, but limiting that to just one muscle group a week. But then again I feel bad when i dont have that fatigue and tightness for 6 more days.

ughhh im just complaining I guess. Been stuck in a $#%@ rut for 6 months now. I know it's not what program you do, but intensity, rest, and nutrition. Yet I feel like I am doomed to be stuck at this level for ever