If you still like how it looks/feels/etc. I wouldn't bother redoing it.
Whether you really need to strip it off will just depend on what it's going through. My more pampered cars can go a long, long time between such "start-overs", as in a year or more. I've just been adding more UPP to my S8 for over a year, for instance, and I don't plan to clean it off in the foreseeable future. Even our minivan (think "daily hard use, year round") seldom needs stripped back to bare paint. Maybe once a year at the very most. But again, my situation might be a lot different from yours.
But note that sometimes the degradation of the finish occurs so gradually that you don't really notice how crappy it has become. Then you do a major re-do and it's a real

when you see how much better it looks.
Oh, and I'd be really surprised if Dawn washed off Zaino. It doesn't even strip wax for me, let alone any of the sealants I use. Rubbing alcohol or a paint cleaner would be my choice.