After further evaluation of the situation and discussing with a couple other handy people, we decided that for now, rebuilding the wall is not needed. It is a finished basement that has no signs of danger at this point. Perhaps over the long run mold or damp might be an issue, but we can see no proof of it now, so right or wrong, we’re going to let it wait a bit.
I did end up building a 2” deep x 19” wide wall segment over the other wall where I want the mount. Dry wall compound is drying and I figure I’ll have patches and taping done and ready for paint by Friday and it done and mounted this weekend. fingers crossed that it doesn’t look too much like an amature did it. The nice thing I can tell so far is that it won’t stand out too obviously, especially once the walls are painted the off white they will become.
Hiding the TV is not a priority at all. Having it out of reach of the 1year old is :). The room is large-ish also, so mounting will allow angling and tilting depending on what other things are going on in there. The TV has a wireless media center, so (most) all components will be on the opposite side of the room out of the way.
Thanks for the advice though. It is something to keep in mind as we make additional plans for refurbing various additional parts of the house.
-- I was a knowitall... until I bought a house