With each major SW release, we resave our templates (part / assembly / drawing) to the newest version.
We have noticed a few small aggravations and one theory is that since our templates date back as far as 2006 just resaving them might be carrying forward unexpected consequences.
We had one problem that required sending sample files to SW. They commented that the file structure dated back to the early days and that may be part of the problem we were seeing. I asked at that time what their recommended best practice was for keeping templates current. I never got an answer.
My current aggravation is the "self rearranging" order of custom properties. SPR 337972 dates back to SW2008 and claims it was fixed by SW2011 SP5. Discussing with our VAR I brought up the idea of artifacts being carried forward in our templates. They thought the idea had merit but had nothing concrete.
So, what is your process regarding template currency when you upgrade to the next major release. Throwing away our current templates and starting over from scratch each release seems really inefficient. The template settings have been "slow cooked" over the years and the documentation of what the specific settings are is the template itself - I don't have it written down anyplace.
There may not be a right answer, but I am interested in learning the things you consider important.