Generally speaking, these upgrades are referred to as NOR1 upgrades (have a look at the URL of the site you are taken to when you are offerred the upgrades, and you'll see NOR1 in there). They are an attempt by Hilton to upsell your room (a bit like "would you like fries with that?"). It's an agreement that if there is a premium room at the time of your check in, you agree to pay an additional fee to be put in that room - for you, it's cheaper than paying for that level of room albeit not guaranteed, and for Hilton, it's extra money.
But my experience as a Hilton Diamond is that you'll usually be upgraded to the premium rooms if there is space available anyway. Different hotels interpret the upgrade policy differently, so it's not going to be this way in every Hilton everywhere in the world, but I don't take any of the upgrade options at all - I leave all of those choices alone and don't confirm anything in the NOR1 upgrades.
As it's a different system to the status based upgrades, I tend to leave it. Often hotels will list a particular upgrade which you would get as a result of MyWay - in my own experience, you still can get better upgrades at check-in than what they claim your complementary upgrade will be on the NOR1 upgrade system.
The important thing here is that how individual hotels use NOR1 is very different - some list your MyWay Diamond Upgrade, some don't. It's extremely variable. But my experience is that I don't offer to pay for extra upgrades, and as a Diamond, I am still well looked after.
