I searched on this and got "general" changes ('00, and then '04...) but what were the year to year changes?

How detailed do you want it man?

mainly where there any major changes from 89-95.  I know with *most* cars it is best to avoid the first year of production while the companies "iron out the bugs..."

Alright since your new I'll break it down for you , 89 only year for clip-ons, 90-91 no changes - Colors available Pearl White (dropped in 90), Italian Red, and Pearl Black. The 91 added Jade Green,and Pegasus Blue.

92 and 93, Higher rate springs and preload adjusters were fitted to UK models, Colors available : Italian Red, Pearl Black, and Deep Purple Met.

95 and 95, Color change only - Light Purple Met., Candy Red, and Pearl Black. Candy Red dropped for 95 replaced with Teal Green Met.

96 - The design of the front caliper is changed, Colors same as 95,

97-00 Clutch switch intergrated into the safety circuit. : Colors avalible 97, Candy Red, Marine Green, Deep Blue, and Pearl Black. Green and Black replaced for 98 with Aztec Orange. 99 - Forest Green, Candy Orange, Phiolina Yellow, 2000 - Candy Orange, Jay Blue, and Pearl Black

Info from Haynes Manual

These links may help
http://www.suzukicycles.org/GS-series/GS500E.shtml
http://www.suzukicycles.org/GS-series/GS500F.shtml