A simple question:
Parts factory costs $550 so I have to produce more than 25 cars to make even its building cost.
So, when is it really useful to build?
New questions should really be posted as new threads. Anyway...
If you are going to end up closing the space with the parts factory, you get back $400 of the purchase price, so you only have to produce 5 cars to make it worthwhile. If you don't close it, it's worth the full $500 at the end of the game.