I love the griddle, as I have one for searing. I would highly recommend one too, but you are getting rid of a lot of variety of meats on a griddle alone, ones that that are my staples. You want to get the flavor of smoke wood you need a smoker too. I love my griddle, but it can't do everything like my Kamado
Pork Butt
Brisket
Whole Chicken
Turkey
Pork Ribs
Prime Rib
Yeah, they're all really completely different devices for different purposes...griddle, grill, smoker. You can get by with just a smoker that also grills plus a griddle. But I don't know of any that can do it all, at least not well.
It's also nice to have a gas grill for quicker cooks. And don't even get me started on pizzas. None of those can do pizza well, at least not without a conversion kit.
Ideal setup:
Kamado - for smoking & charcoal grilling
Gas Grill - for quicker grilling
Griddle - for griddle cooking
Pizza Oven - for pizza