its really up to you. Note that the outer ring, if explored, will make updates to the last 2 biomes fail, so you want to not go there.
1/3 is a lot of territory, and it may be time to see something new.
partly depends on how attached you are to your homes and favorite bashing locations, or if you want to explore and wander at random and are running low on places to do that.
You can always go back and forth... so a new seed isn't like you deleted the old one or anything.