Been Diamond for 12 years. Due to business travel.
Have enjoyed some of the perks, especially European breakfasts and lunches.. (The USA, ugh....stale tepid water, again??)
Now retired, will still take advantage of Diamond another year but beyond that I don't know if it's worth the annual spend on my own dime.
I have a Sapphire Reserve and since the points are usable so many places maybe that's enough.