I mostly use Tidal these days and some of my old CDs and Audio DVDs. Spent half of today listening to different stuff - rock, pop, piano, vocals. With Center Stead not working in most cases with center Speaker it sounded not great for 2 ch and actually very good for native 5.1 recordings.
Then I discovered something was wrong with the receiver as some of the settings did not have any effect on sound. I did factory reset, new calibration. Still no ypao, just levels and delays. Now avr works fine. Center spread works but I put center image param to its max value 1 (it can be between 0.1 and 1). Now in some cases for 2ch upmixing I like center even more than without it. In about 30-40% I hardly can tell the difference and about the half of recordings with actual center sound worse - less mid, less bass, too narrow sound stage.
As you said it is difficult to predict what you get. Try and error. But at least there is a choice. And at least for movies the center was worth to buy. The dialogues are much clearer now.
What center image value do you use for center spread?