Recently bought a house with some rooms having very amateur remodel. History: house is built on a hillside so second story is the main floor. Main floor is typical wood subfloor. Kitchen and bathrooms are done quite well with properly thinset 1/4 durock and tile. Main living and bedrooms done not well, with 1/4 plywood, screwed down for leveling and beautiful nailed down engineered wood. Wood subfloor is showing signs of age with dips from traffic in some areas and generally off level in small areas which feels wimpy and creaky. Need floors between rooms level for wheelchair so i need to keep up 1/4 space between rooms. Since 1/4 plywood is worthless here, am I crazy for considering leveling compound to eliminate dips and low spots, 1/4 durock thinset and screwed down next for added durability and sound dampening, followed by recycling this gorgeous Brazil Koa by using nice quality glue trowled down to the durock followed by this engineered wood? Im handy with tools and im no stranger to construction, however im not too interested in replacing the subfloor. Doesn't seem necessary if this method is feasible. Any thoughts?