It's interesting to see the variety of responses.
I appreciate everyone's input, even the poster(s) who were irritated at my somewhat negative opening post.
I've become increasingly negative toward Sonar since the switch to X1. Not like forum troll negative, but just internally grumpy. It's like those makeover "before and after" photos; some people prefer the "before" photo, and other people prefer the "after". I personally prefer "before" in the case of the 8.5.3 vs X1 change. In my case, it's a purely subjective preference based on my personal experiences with the pre- and post-X1 versions; I had experienced fewer frustrations before X1 than after. That's all.
Anyway, thanks again for the input. I'll almost certainly end up upgrading to the new version at some point. It's just a matter of how long I'll stick with X3 before taking the plunge. The longer I wait, the more money I'll save, but if there are significant fixes to the UI in the things that I do, I would be willing to upgrade sooner rather than later. I'm guessing I'll have to drill down into specific issues to see if they're fixed in the new version; there doesn't seem to be a general declaration that the new version completely fixes people's problems with the old version.