It's one of those things that you'll never really know. Part of it is property-dependent, part of it is occupancy for the nights you're staying, part of it is dumb luck--maybe a wedding party booked all the suites in an otherwise empty hotel.

When you get an amazing upgrade, is it because of your status? Repeat visit history? Rate you booked? Total luck of the draw?

Likewise, if you get no upgrade at all, would it be different if you had higher status? There's just no way to know. In general, I think you've got a better shot with a higher status, but there is literally no way to do a cost-benefit analysis to determine if it is worth spending more nights and dollars in a Bonvoy property to move up in status based on guaranteed improved future treatment.