Ok, so I had a performer and still have my 18.5" WSM. I got my WSCG to replace both. Now I have been able to replicate most my performances on my WSM with the WSCG. In fact, I find the temperature control on the WSCG far superior to the WSM. I can consistently dial in temperature settings between 200-300 f and maintain them within +/- 3 degrees with little or no effort for hours on end. Plus it uses a lot less fuel then the WSM. So it has effectively replaced my WSM (which I kept for use when entertaining and need multipule cookers).
Regarding it as a grill, I can get the temperature up to ragging hot >600 f. I was reasonably sucessful in cooking a pizza , and some burgers. I cooked steaks for the first time, but they didn't come out like I hoped. The bottom line is I haven't come up to speed on using this as a grill. My two issues are bringing it up to grilling temperature quickly (it takes a good 20-25 min with gass assist on grill setting), and how and when to keep the lid open or closed. So, I haven't got to the point where I can do on my WSCG what I could do on my performer. I do attribute this to operator error and coming up on the learning curve as the WSCG is so much more efficient and better insulated than the performer and I have yet to adjust my cooking habits to these differences in grilling performance.
Regarding the use of the rotisserie, I have never used one so I can't comment on it. I suspect, however, that it's effect might be approached if you cook with the charcoal grate on the lower level, but with no diffuser plate. Almost like the WSM with a hanging rack and no water pan so you get the radiant heat effect. I have yet to try this, but it's on my list of things to try.