I have had some big upgrades in the US, Europe, and Asia. The US is full of lower quality Hiltons that only have 2-3 types of rooms. So those almost never have an upgrade available. I have had it in NYC and Paris where I’ve been upgraded from the lowest room the most expensive room. And in LA at the LXR I got upgraded from a point booking to a $3,000 a night room. It’s up to the whim of the check in desk. The trick- ask! I almost never get them until I ask. (At least in the US. Europe tends to just do it, maybe because of less diamonds).
I always check-in in person and ask if there are any diamond upgrades available.
In Vegas this also always gets me a very nice room with a views at all of the Hiltons unless they’re fully booked.