Just go cheap on toilets or clean existing.One inexpensive technique I've been using more lately (even in bathrooms) is Board & Batten on the walls or "shiplap" look with MDF 1"x 4"s (oil based primer for humidity protection). 

@Robert Smith Is there gravel underneath?

Just make sure you buy one as previously stated with the padding underneath.

One was a mounded system because of soil that wouldn't perk and required the removal of several large trees. 

The soil pipe is original to the 1950 home, so I may replace that too.

Does it work to just install the Luan over top of them - ie. does it retain it's firmness / smoothless and not eventually conform to the irregularities underneath it as well? 

Very similar climate and soils to Central Valley CA. 

Underneath the carpet was those thin width hardwood floors.

We are interested because its a property that (2) two bedroom apartments and 3 storefront underneath.

You draw a T on a paper, and you put what you are giving up underneath one side of the T, and what they are getting in return on the other side.