How much energy does a cell expend maintaining its contents?
I'm going to take a stab at this.  Its a difficult question to get right, just to put is in the right mood here.

Lets leave energy out of this as the proper term is structure.  The cell is designed to compartmentalize itself to differentiate its own living tissue from other cells.

In this regard Alan Kay's analogy is pretty good.  In multicellular organisms, individual cells (mostly) each maintain their own DNA and energy storage, though they get their nutrients and energy from outside.  They create the organism as a whole by differentiation; each cell changes to take on a specialized role and depends on other cells to support it. E.g. in animals some cells/organs digest the food and distribute nutrients to the rest, others form the lung and help distribute oxygen and others scrub the blood of waste.  

This is somewhat like good code design where functions are partitioned out into specialized parts of the software for the sake of maintainability and organization. 

Somewhere after this point I think the analogy breaks down since after all the point of good coding practice is to organize the code for understanding within reasonable human conceptual limits.  The cells and how they organize themselves are still plenty mysterious to us as they have their own definition of roles and function much of which is still being discovered today.  For instance the many kinds of neurons in the brain and the sorts of structures they form are extremely diverse.  We have few organizing principles for predicting how many cell types would exist in a system and these only create partial answers. 

After all its just an analogy...

getting close to an answer?