What ways have you heard the 8 speed system was better? I've only heard that the 8 speed chain is beefier and thus less likely to break and the shifters are less complex and thus more robust. If you aren't breaking 9 speed chains, I wouldn't worry about it. You could always go test ride an 8 speed bike at the LBS.
If you really want to try 8 speed on your exact bike, you'd need the chain, cassette, and an 8 speed rear shift lever. You could probably get a 9 speed rear shift lever to shift an 8 speed cassette but any benefit of the 8 speed shifter is lost then.