Kenny,
I know nothing about the Egg, but I have a performer kettle and wouldn't take anything for it. It's the best grilling machine I've ever had, and that's a lot! And I too bought an 18" wsm for the smoking edge. Yes, you can smoke on the kettle but limited amounts and not nearly as well when you master the wsm. Do I still use the kettle to smoke? Yes, when I need more than 8 racks of baby backs, which is rare indeed, but I can do 3 more on the kettle. But I can do 6 8 lb butts on the wsm and feed 90-100 depending on other factors. Plus, the indirect nature of the wsm makes if far superior to the kettle as a smoker, in my simple opinion. So I answer "yes", you won't find a better charcoal grill than a kettle, and "yes", the wsm is definitely worth the upgrade in smoking. These are just my opinions and not stated as orthodox fact, but I'm thrilled with my results.