CS 5 upgrade - is it worth it ?

Another reason you may want to stick with (or at least keep around) your copy of CS5 is if you have some plugins that are no longer being developed, and won't work with newer versions. I keep a copy of CS4 on my computer for this very reason.

CS6 is every bit as obsolete as CS5.Both are "thrown away" if you want to put it that way.  Many, many versions behind, and software makers move on whether you do or not. If you are happy with CS5, and happy to keep running old systems to keep it going, I see no reason to "upgrade" - even if you can find someone selling a genuine and unused upgrade (used upgrades are not transferrable, and there are many fakes).

Are you aware that the current version can be had for US$10 per month, with upgrades includes while you subscribe? (Cuts off when you stop)

It seems a bit of a harsh, I've already paid for CS5, from what I've been told that's disregarded, thrown away.

And nobody is stopping you from making use of Photoshop CS5.

But Photoshop CS6 has been obsolete since the release of Photoshop CC in 2013, so it might be a problem even to purchase an upgrade.

If you chose to stick with obsolete software (CS5 or CS6) you may want to »lock down« your system because any change (OS, drivers, hardware, …) might break the set-up. So make sure you can roll back any updates or hardware changes you make.