The value of Diamond for me has been the GUCs. If you’re only flying domestic you can also get a huge pile of RUCs.
There’s probably also service benefits but I luckily haven’t had much trouble (though some people swear by them) so the only time it mattered to me was when a bored driver took me out in a Porsche to play on the tarmac at Seattle during a long layover.
i am higher on the upgrade list for sure but I’m not sure it’s made a difference on my routes; that is heavily dependent on your flight patterns.