This is from my standpoint living in central Florida. I tend to see more stock motos than ICC’s….but I believe that may be a regional thing. As far as cost goes, that depends upon how competitive you want to be. Sure, you can run and ICC out of the box, but I believe most of the competitive guys put the upgrade kit on them that cost more. As far as run time and performance, I have never run an ICC. With the stock moto, again it depends upon how competitive you are. There are guys that do top end rebuilds every 1-2 races, but I think you should be able to get 10 hours out of one. Some will say the cost of a rebuild is not worth chancing it and having it come apart at hour 5-10 and doing more damage.
As I said, I have never driven an ICC so I have no experience with one. But it pretty much holds true with any motor, the more competitive you are (or want to be), the higher your cost are going to be.