I am normally Gold via credit card. I currently am Diamond via stays, but I haven't noticed much difference, except for one thing, I earn 100% bonus vs 80% bonus with Gold.
I haven't been upgraded in most stays (although most stays are at Hamptons and Hilton Garden). My only stay at a full service Hilton was in Boston where they promised a $15 credit, but only gave people a $10 credit (that was disappointing, but not enough to ruin a fine stay).
But, I have earned a ton of points with the bonus, the promotions, and the credit card. I have some awesome redemptions planned this summer in fantastic properties in Europe using the 5th night free. Maybe my Diamond status will give me some additional perks then.
I didn't actively seek out Diamond, but I will take it for the additional bonus and just maybe, one day, an upgrade. Plus, I can park in the Diamond parking at Hamptons more often
I have tried the Marriott program and have gotten some value out of it, but not nearly as much value as I have gotten out of the Hilton program (based upon my stay patterns, and my priorities).
I don't value Diamond enough to get it via an expensive annual fee credit card, though. So, I agree with most of your points, but wanted to add the benefit of the points bonus.