Maybe somebody can provide a more current view on the subject.
In my opinion, renewing temporary residency is pretty much automatic - no questions are asked at all. When you apply for permanent residency, you undergo an evaluation. They are more concerned about something called "medios lícitos de vida."
Basically, you should be able to demonstrate that you can support yourself by legal means. This does not necessarily imply full-time employment. If you can make a decent living with a part-time job without burdening the system or requesting support, that's considered to be acceptable. Or if you won a lottery at some point and that’s enough to support you for the rest of your life, that would probably also be OK.