The first Adobe Photoshop CS version was released more than a decade ago and throughout the years, Adobe continued to make significant updates to their flagship product. However, the upgrade prices were pretty steep resulting to some people not upgrading until absolutely necessary when OS compatibility becomes an issue. But Adobe shifted to the Creative Cloud model where the price becomes more bite-sized but you have to pay either monthly or annually for less. For some professional designers, upgrading could be a waste of money since existing owners of older licenses can keep using their Adobe Photoshop version forever. Plus older versions starting from Adobe Photoshop CS3 don’t feel outdated and they still work fine in OS X Mavericks.
If you are indeed using a fairly old version of Photoshop like CS3, trying out the trial version of Adobe Photoshop CC would be the best decision since there is a 30-day trial available and you can experience far more features ranging from a refined interface to better performance for newer Mac systems. Adobe Photoshop CS6 is a more refined version so the transition to Creative Cloud may feel like a light upgrade so it would be better to read exactly what new features Photoshop CC brings to the table.
On a final note, it is worth noting that while you need to keep paying for Adobe Photoshop CC, you will always be treated to the latest version. This means that Adobe could roll out new features at any given time to make the upgrade from CS6 even more attractive.