Honestly, it depends on the watch. A couple months ago, I won an auction for a lot of 6309 parts. I wasn't expecting very much, but when the parts arrived, they were in pretty good shape considering what I spent. I cobbled together some other parts from a 7002 project that failed, as well as a AM 6309 dial I got from mmounce, and pieced it all together. I also did what I'd consider my first real movement service. So for less than $50 total, I've got this on my wrist and it's now among the most accurate watches I've got. Of course, she isn't pretty . . .
Contrast that with my even cheaper 6106-8100 project, for which I have got to great lengths to make almost perfect. In the end, I guess it depends on how the watch wears its age. If it looks like petrified wolf sh*t with only a little wear on it, I'd likely try to get it back to 100%. If it wears its age well, then I'll just leave it be with all the "ugly" on it.