OP... I do both SHOT by SHOT correction, to bring each shot to the same relative quality, brightness, etc. After that, I do a a final pass of curves for LOOKs across the top of all the clips.
here is my work flow.
Edit -> Finish and lock edit -> shot by shot color correcting -> color for look and feel of entire film.
to elaborate, the first pass is NOT to tweak the look, I don't crush blacks or anything like that, I just even things up so that all the shots look about the same, maybe a little bland. If there is something like a blow out for the shot, etc I can mask the area and "spot" treat problems, but never pushing it to a particular look.
Once Im done with that, Ill add a new curve over the TOP of ALL the clips, this is where the magic happens and the look and feel is enhanced, it helps to make all the clips look like "part of the same thing" there is a certain amount of going back to the original clips and tweaking the curves for them, but not a lot.
Hope this helps