So... I've posted the following video to illustrate the issue I've always perceived as a generic and horrendous show of performance re: Opus' metadata reads from mp3's.
Since posting that video... I actually realize it's not even dependent on the wildcard path format I'm using, it seems to basically just be tied to....... Libraries vs physical paths.
What I meant about it not being related to the wildcard path format I'm using was just that it's what I was using to get the format to show the metadata columns in my example video when I clicked into the directory to show what happened.
But the same thing will happen if I turn on the same columns manually via a favorite format after entering the directories (in some other path than that which triggers my wildcard format).
Confirmed. It seems like the combination of MP3 tags (doesn't seem to happen with WMA) and libraries is causing Opus to read all the MP3 files from start to finish to get to the tag data near the ends of the files, while in a normal folder it jumps to the end of each file without reading all the bits in between.
Not sure why yet, but we'll look at it.
Thanks for the confirm... sorry I never piped up about this more. I switched over almost entirely to using Libraries for media management, so incorrectly assumed it was just a generic issue with the use of taglib or something. Even with all of the library specific stuff I found in early v10 - I never would have thought this was something that would have been tied to libraries. 
Beta 7 has made huge improvements here... thanks!