Hilton's policy leaves a lot of flexibility for hotels regarding the upgrade policy.

Some hotels have dozens of room types, so being receiving a one-category upgrade may mean you go from a low floor to a high floor, or a parking lot view to a "resort view", etc. The language also says "may receive", so temper your expectations and you'll be happy with whatever may happen.

As a data point... I have 300+ stays and almost 900 nights in the last 10 years. My upgrade rate is < 3% and that's up a good bit over the last 12 months.