A systematic review already exists in the literature. When is a newer one required? Suppose that a systematic review on a topic X was published some (3-8) years ago by someone else, and it is currently still a useful source for what has been made before it was published. However, more recent works were also published later.

Generally, how can I decide whether it is a good idea to work on a newer systematic review for publication, taking into account that the newer review could be (somewhat) similar in methodology and would be based on extended and more recent literature (including that already reviewed in the published one)?
When? 


Whenever there is a set of papers that has significantly extended or changed the topic of interest.
If you have to do it as part of your thesis.
If you are contributing with a new approach/method in a publication (the literature review would typically be part of the Introduction).


My advice: do not spend too much time on writing and trying to publish a literature review if the problem has not evolved significantly during this time. Most of this kind of works get lost in an ocean of surveys.