From what I understand:
- v18.1 changed a lot of things in the battles from v17.2. If you have battle scripts, chances are you cannot update them easily.
- v19.1 changed almost everything else from v18.1. If you have general scripts, chances are you can update them, but you'll have to do it yourself.
From what I see, the third type script could be adapted (but you'll have to think a bit). As for Birthsigns, I don't know ^^"
I started making my game in v18.1 and a few months later, v19 was out. I refused to upgrade because I had ~30 custom scripts ("custom" = made by me). In your case, if you don't have custom scripts, you should upgrade to v19, because if new scripts are released, they will be for v19, not for v17, and you will find less help with v17.