I am also 90% audio-only. I have upgraded MC every version since MJ 6. For years the subsequent versions got better and better for me (I think I influenced Matt to implement one little thing that is hugely important to me). But since MC 15, I've upgraded every year because I appreciate the product and want to support those who create and support it.
Because, my AUDIO tagging work is still done in MC 15.0.122. I treasure it, make sure I have it available for re-install if needed, and I'm using it right now on my AUDIO-devoted PC. It was the very next MC version that removed what I consider to be super-efficient keyboard-oriented tagging, and replaced it with (again for me) time-consuming, multi-click, clumsy "searching" even though I'm NEVER "searching" my own tags, I don't need suggestions, I just need to select the tags I long-ago created that apply to a particular track (64K tracks and growing). Back when MC15 was current it was discussed that the tag search should be in addition to the long-standing tag selection mode, but alas search-first replaced direct alpha-jump selection. I tried, but find it massively frustrating to tag in any later version, but I keep buying them (paid for MC16, 17, 18, 19, 20, 21, and now 22).
This is my long way of saying, there is still room for improvement in managing and tagging, and it probably applies more to Audio because so many audio libraries are large/huge, and because there are (for me) so many important ways to tag. I use about two-dozen standard and custom tags (the reason Pane tagging isn't helpful, not enough screen space, plus it's slower than keyboard tagging).
Proper one-time tagging is essential to using my music library in all the ways I desire, or that arise. (I should mention my years of programming major radio stations, where I devised a music categorizing/organizing/selection system that I still use via MC. When my High School Reunion organizer called, asking if I could provide music, it took me about 1 minute with MC and my tags to identify all the hit songs that would be suitable by year, then subset for mood and duration and a bunch of other factors. At the event, MC and my music on my laptop provided the perfect mood.)
I say 90% Audio because I also use MC for IMAGES (photos), especially now that Google has abandoned Picasa. MC allows more efficient image tagging and organizing than Picasa, though Picasa has cool features (facial rec, image editing) that MC lacks. The big room for MC improvement is tag name/format compatibility, discussed and debated over the years in this forum. It would be really nice if MC22 provides some Images mode enhancements. With Google Picasa Windows app becoming defunct, and Yahoo Flickr being a dog (and the entire company for sale), MC seems to have a big upside opportunity.