The software has gotten a lot better since I started using it, but I have also gotten better at using it.
That's really the odd thing about digital photography vs film. We're really still pretty early in the digital realm...film had well over a century to evolve while digital is really only about 25 yrs old (and that was crude back then).
While film was essentially "fixed" when developed, about the only thing that could happen was bad stuff...scratches, mold, fading, destruction, etc. So, one shot and processed, a neg never really ever got better...
Fast forward to today and the tables are turned...using the best post processing (raw pst processing plus digital manipulation) Older digital captures do indeed get better with age...now processing, new noise and sharpening and new algorithms mean that raw captures done decades ago can now be processed much, much better today than back then.
It's a whole new paradigm that requires a new way of working. If you've spent a lot of time on older images and are happy–fine, roll with it. But, just know that what you can do now could be way better than what you did back then.
I see this a lot in my own work...sometimes it's really worth a revisit (starting from scratch with a raw file) and sometimes it isn't. This decision is yet another way of "expressing your vision". Don't be afraid or lazy...if the processing has improved and your skill set has as well, don't be afraid to go back and revisit old work. But if you are truly happy with old work, don't let revisiting become a neuroses...
If it helps the work, do it, it it doesn't move on to something new :~)