Heating mats were used a lot years ago but not so much today as plants can grow just as well without them. IMO
they were a pain and yep a total tank tear down was needed if you wanted them out or if there was a problem.
As for vermiculite I think many use it when mineralizing soil for a dirted tank. Personally I just like to use Organic Potting Soil and deal with the excess nutrients being leached into the water. I see no need for it at all but that is just my opinion.