So.. one of my shifters is shot, its old shimano 600 so its had a good life. Talking to the mechanic at the shop it sounds like my options are either buy new 8 speed levers which would cost me ~$140, or I can spend a little more and upgrade to 9speed 105 parts.

To go to 9 speed, I know I need new shift levers, a new cassette, rear derailluer(?), and chain. If I only upgrade those parts, will I have a smooth shifting group? Or do I need a new crankset/front derailluer also?

Also, as I was checking out prices I saw a lot of RD's said 8/9spd. Will my shimano 600 RD work with a 9 speed group too (and work well)?

Thanks in advance.