I always keep Home Assistant as up to date as possible. Home Assistant keeps improving a lot. Month to month each update goes fairly seamlessly if HA is kept up to date, but the further it falls behind the harder it is to catch back up. Recent optimisation improvements have also made the update process faster.

If you can make the time it's worth the effort. Even if you have to "start over" somewhat there is probably a lot you have learned since that you can use to improve your setup.