What is the benefit of flashing to latest software?

Well it all depends on what you use your box for.
Most modern plugin will need modern software images.

Me personally as a plugin designer and skinner have decided I am no longer supporting older python 2.7 images.
So that means anything older than openatv 7 will probably not be able to update any of my plugins in the near future,

But if the plugins you are using are still working, then you don't have to keep updating to newer images.

It is entirely up to you as the user.

Your box is a little old now and not very powerful compared to modern boxes. (great box in its day though) Maybe time to put some money aside for a new box.

But if you are not clear of the update process I have a setup guide here.
OpenATV 7.* setup guide by KiddaC