I personally would not want to lower the opacity. Typically we color correct scene by scene. I almost never apply a single setting to a whole project. The methods you are using seem to be correct. Lowering the Highs (whites) and Mids will lower the percieved brightness (luminosity) of a scene. You might want to use a filter such as a broadcast safe filter and see if that improves the result. But again you’ll have to apply that scene by scene. What seems to be the problem that you are correcting?
It sounds like much of the project may have been over-exposed. When we shoot in the field we reqularly under expose slightly. That way it prevents loss of detail in highlighted areas. And as a side benefit it prevents the problems you may be experiencing now.
Richard Martz
MagicMartz Media
Final Cut Pro HD
Kona LH
After Effects
PhotoShop
Illustrator
Lots of other Fun Stuff!