Dee Dee,
lightening a shot that's underexposed by a half stop isn't really all that big a deal nor does it normally add much noise. I purposely underexpose my stuff by at least a half stop to ensure I don't blow out any highlights. When I bring them back up, they're clean and noise-free.

What ISO are you shooting at? JPEG or RAW? I have to admit when I first looked at the images you included for examples I wasn't all that concerned about the exposure because it could easily be brought up in PS. If you're brightening in PhotoShop, what kind of color casts are you getting?

Jim