Between paying off your V20 and the $$$ for a new S8 you could be looking at over a grand (!!!). Thats nothing to sneeze at.
Here's what I would do... go through the various trouble shooting steps and procedures to try and re-gain your battery life and text messages (if you haven't already). Clear cache, memory, delete un-used apps, scrub through permissions and even a factory reset if thats what it takes. Hopefully you can fix whats gone wrong with that latest update... or at least buy time for S8 discounts and perks to start rolling out. The S8 phones are still new enough that there are no deals and discounts yet.
FWIW Verizon updated their message+ app a couple months ago it became unstable on my V10. So I deactivated it and switched to android messages and it works much better. I never once thought it might be the phone... but it could have been for all I know.
Good Luck!!