A mistake I made when I was a newbie (I still make mistakes) was I repaired the drywalls and then had the foundation for a pier and beam house repaired which introduced new cracks once the house was leveled. so needless to say I had to repair the walls all over again

Sounds like your on pier and beam and if the floors are livable as you have describe, i would not do any thing to the floors.  

Older houses will have pier and beam to allow for movement. 

The seller disclosure states that the house has had foundation issues before, but was remedied with support beams.

We also added a privacy fence around the property and reconfigured outdoor living by moving a beam from the center of covered back poarch to on the side, providing a large open outdoor living area.

One was partially renovated, but the renovations looked sketchy (20-inch wide shower, rippling siding, exposed lam beam in the living room hanging down about 10 inches, etc.).

If you are dealing with an addition built on 12" beams (or if the original foundation is old and not built to current standards), the repair company might not be able to push the piers down to refusal depth or psi due to the beam not taking the load, thus leveling it, but not guaranteeing it will not continue to move in the future, thus not providing warranty.9.

It is a pier-beam home that caved-in at the center of the house!

So you now get to pay for structural supports likes headers and beams and posts...just like a stick built building. 3 - You still have to meet all the same building and energy codes.

About 15k went to steel i-Beaming the entire basement due to a failing foundation wall.