Actually, the machine zone is available no matter which of the ranches you are on. It is the holding area for all of the machine houses that are gradually added. The machine houses hold different machines for example the baker, etc. The main perk of the machine zone is that you can set up something to work that might use several machines. The machines can be told how many items to make. It uses time units which are purchased with gasoline. (For example, I will turn 10 gallons of gas into 700 time units.)
You asked about disappearing...yes sometimes you will have a glitch where the entire zone disappears, BUT you just have to refresh or go out & come back in and it usually fixes itself.
You also can take the machine houses out of the zone, back to the ranch and rearrange them. Also, if you want to take a machine out and set it up on the ranch just to work it manually it is easy to do.
Yes, it will cost RC's to upgrade your machine houses. I have upgraded some of mine. So far, one fully upgraded machine house will hold 95 machines.
Personally, I love the machine zone.