Should I use a regulator to improve efficiency or safety
Efficiency

A regulator can't improve the efficiency.  [I have to reconsider this.  I need to think about the buck.]  

A regulator will have losses.  A regulator will have quiescent current (which varies a lot from one regulator model to another).

Safety

A regulator can prevent over-voltage of the downstream circuitry.   However, there are other protection methods aside from the regulators.  Be aware of the leakages in the protection circuits, include the leakages in your power budget.

Performance

Whether or not the varying supply voltage will affect analog circuitry depends on the specifics of the analog circuitry.