So far, so good with the subscription.
When the update became CC2014, I put off cutting-over until now so that I could slowly bring my plug-ins and actions and then take the time to set it up properly. Now that it is done, it seems to work just fine and I really like the auto alignment guides since I also use PS for design and composites.
I still have CS6 and older on my system but finding I need them little other than as a back-up to use if circumstances require it. I still use CS6 on my Macbook since I only use that for demos and presentations a few times a year and it is becoming an antique anyway.
If you don't ever plan to upgrade your digital cameras, computers, etc. and CS3 does the job an you are happy with the results, why not keep using it until the very end? However, if you get a new computer with a newer OS, etc., you will need to make the leap to the newer tech. It's just the price we pay in working as pioneers and slaves to the tech we now use for our craft.