The FZ6's are great bikes, I've owned a couple.
I had a Corbin seat on my 04 and it didn't seem much better (aside from looks) than the factory seat. I did have a Puig double bubble windscreen on both bikes and it was an improvement over stock for me, I'm 5' 10". I ditched the fairings on the 04, rode it for a while, sold it, then ended up getting the 06 about a year later. The biggest and cheapest improvement made was going down to a 15t front sprocket.