Oh, very much. Once the source material has ended, there is a much more solid foundation to write. Even though most fanfic ends up AU, it feels more satisfying to keep it as close to canon for me. If the canon keeps changing, then my clever insights are for nothing… That means I like writing in that sweet spot where the characters/story I like are finished in canon, but before other fans have lost interest. It looks like Potter and Star Wars will be active for a long time. Bur Buffy and STOS are slowing. I like exploring where canon doesn’t have the time or interest, especially after the ending where there is the freedom to do whatever I want and all the canon is available as both problems and history.
Since I’m now on my third writing fandom, I find it interesting to start getting an idea of the bell curve, the activity level in writing activity across different fandoms. Some books/movies/game releases can choke a living fandom. That is another risk a sa writer, do you incorporate a later release? I know the ending before I start, but my muse has starved when the canon was a desert. (OR writing a fanfic for a MMO end up feeling just as pointless) Keep writing, as long as you are enjoying it. Keep posting as long as people seem interested. Measuring that interest is the tricky part for me.