EDIT: This is what I do with an already clean kettle, to keep it lookin good.
I try and keep the outside of my daily cooker (Performer) lookin as sharp as I can. I keep a tube of those disinfecting type wipes on the bottom rack and give the kettle and table a wipe down after I'm done. I use a damp paper towel to remove the soapy film off the kettle afterwards. All that takes literally less than a minute to complete. I also use my grill cover, if I'm not gonna use it for a few days.
The inside of the kettle just gets the ash removed before each new cook. I'll occasionally scrape off excess gunk, melted cheese, sauce etc, if it's getting outta control, with a plastic putty knife. The inside of my kettle has a very nice buildup of "seasoning" and shuts down very nicely! I have never had a grease fire (yet) either