I have been diamond member for years, mostly staying in the same hotels, year after year. I would second ajp76054, you will see upgrade mainly from hotels, where you are a frequent guest.
When I visit a new hotel, there are no upgrades or other perks.
If upgrades, perks are important for you , another chain might be a better choice.
Otherwise the only benefit is the 15% bonus for plats, 30% bonus for diamonds.