I think I want to stiffen the front end up a bit. Those forks seem to blow through their travel pretty quick. Being the cheapo that I am, would  this produce any type of worthwhile results? I had a KLR 650 and put some PVC spacers in and it seemed to firm things up a bit.

If so, any suggestion on Diameter and the length of the spacers?

Thank you

The stock springs in the gs500 are single rate meaning that adding spacers and compressing the springs slightly will NOT stiffen them. but adding spacers will pump up the front end slightly giving a little more suspension travel which can help with bottoming out under heavy braking.

depending on your weight, thicker fork oil may help however, I am 170lbs (180ish with gear) and 20 weight oil (stock is 10w) with 1/2" spacers made the front end better. not great, acceptable is more like it but much better than stock. if your over 190# I would just get stiffer springs ($80) and 15 weight oil.

If your under 150# 20w oil and some spacers would probably be close to perfect.

If I was to do it over again, and I just might, I would just get stiffer springs and 15w oil.