Applying KonMari directly to hobbies has to be done with many concessions to your own personal goals and needs.
I had issues with defining my personal meaning of 'spark joy'--if you put any item from my hobbies in my hands, I can think of something to do with it. I had to learn to ask if it's something that I, specifically, would/could/wanted to do.
I had to learn to ask if, yes, I could/would/wanted to do it, was I willing to do it for the finished item, or just the joy of doing the craft? Because, I had to remind myself, I could get that Joy Of Doing just as much from things I'd want to keep as from things I wanted to do Just Because.
And maybe that's not an issue with your own way of doing hobbies, but, absolutely, it is for me and mine.
So I had to redirect my brain from a generic "What would happen if..." to a more specific "What would happen if...with these materials I actively like," and not just with stuff I have around because it was a bargain/gift/something I've had in the craft stash so long that my tastes have changed
And, yes, there is a big tendency to think, "But if I use The Good Stuff, then I might ruin it!" I had to prod my brain back with "But you probably won't ruin it, and then you'd have something you could use made from this Fantastic Craft Component, instead of just sitting in storage where you admire it while looking for something else to use that you won't mind if you ruin."
And, also...sometimes I'd use 'lesser materials' and end up with something I liked, but, mostly, I'd end up with something neutral to actively regretted.
I do know that I have had enough experience with most of my hobbies that I can, most likely, make something without ruining it--and if I do mess up, I also have the knowledge to salvage it. And I learned those skills by using 'lesser materials'...but, also, I learned those skills in a time when my tastes weren't as focused as they are now, and the things I had then that I might consider not suitable today--either due to the actual item quality or just the color scheme--were completely suitable for me then.
It's not changing tastes as much as refining them, based on getting to know yourself, and knowing what makes you happy to have around.
That's the basic idea behind KonMari: learn what you like to have, and what you will actively use in the future, and keep that, and make its place in your life more prominent, so you will have and use it. Everything else can go, but KonMari is not about figuring out what to let go, it's about figuring out what to keep.
And, yes, there is often deep guilt about getting rid of things--I paid for that, so getting rid of it is the same as wasting money! (even if paid for it ten years ago from a bargain bin.) Someone gave it to me, getting rid of it would disrespect their generosity! (even if it was never quite my style.) It was a once-in-a-lifetime thrift find, if I hadn't bought it it would have languished, unappreciated for what a spectacular (probably vintage) thing it is! (it is not your job to 'save' things from the thrift store.) But what if I want to make something for someone else whose tastes it matches exactly! (c'mon, Brain, you know that's a reach.)
Telling myself that letting it go means that it can get into the hands of others who are more likely to use it has helped me a lot. And, yes, I admit, having the thrift store specifically dedicated to crafts helped convince me to let go of a lot of craft stuff (especially fabric) last year, too, and I know most people don't have access to that kind of thrift store. (My brain would rather roll up to a thrift store and drop things off on my own schedule than have to deal with arranging to meet someone via Freecycle or research what individual groups are accepting that kind of donation.) (And, yeah, I still have two huge bags of fabric scraps, because the craft thrift store won't take those but my brain insists they're still useful...just...not to me. I have a smaller, curated box of fabric scraps for me.)
A side effect of learning to analyze what I already have in terms of "do I genuinely like this, and will I ever actually use it" has been that the same filter is in place when I consider a hobby-related purchase now, too, and I have been able to stop myself from buying things purely because there's an impulse of joy when I first see it. Well. Mostly. The 10¢ patterns at the craft thrift store I have been somewhat reckless with... But they still fit in the storage space designated for patterns, so they haven't yet rolled over into Clutter That Erodes Daily Happiness.
This is how it's working for me; it might not work for anyone else, but, then again, it might? And that's why I share. I have been happy figuring out how to focus on the things I do like and let the rest go...and I still have a completely ridiculous craft and hobby stash that will fuel projects for years.