1998 Co-Pilot, 8 speed with bar-end shifters. The left (front) shifter went out on us today.

It looks like we can either replace the shifters with another 8 speed set or change to 9 speed. Since it was just the front shifter that went out, I can replace just the front & leave the rear alone. However when it comes time to buy a new cassette and/or chain, I could then change to 9 or leave it at 8.

What are the pros/cons of changing to 9 speed? Aside from one more gear, is 9 better than 8? Is 8 more durable / reliable? How about the eventual availability of 8 speed cassettes chains?

Thanks.