Years ago when agoda was leading the pack and I was a frequent user, the money back was quite considerable and could be spent towards getting a better room or hotel or adding days. More recent, post-Covid experience looks like they offer tiny cash back rewards that have quick expiration dates.
With regard to the OP's problems, when any of my registered cards expired on agoda or any website, I don't renew them. I prefer to do one-off charges as needed and option NOT to save card information. The extra time or inconvenience is minimal. I don't trust the security offered by commercial websites no matter how much they say it's safe and secure.