Here is a link about doing the stock suspension without GV.
http://www.ablett.jp/bikes/vtr/vtr_sus.htm Roger is the same guy that helped me to get my frontend setup. 100% great guy!
It's not absolutely necessary, but if you keep an eye on Ebay you can pick them up cheap. I got mine new and unopened for ~$82 shipped. If you are going to be tearing into the forks then why not do it all?
I keep looking at shocks, but my wife's head would explode if I dropped that much cabbage on a shock right now.