I’ve read similar opinions, like “Moving from one system to the other should be done manually“. The indent of that statement is to make you go through the notes and discard what is not needed.
I’m a bit torn. I want to import my 8 years worth of notes from Apple’s notes app in Obsidian so I can discover them with the Random Note plugin, but I also want to go through them and clean up the junk, instead of moving that junk to the vault.
What I started doing is import the notes one by one. It is slow and tedious, but is a process that turned out to generate new notes 
My end goal is to have my vault contain only curated, refined, evergreen notes. But that’s not an absolute. There is a spectrum. The transient, raw, mindless notes from the dumping ground are the soil for the new polished notes. In between the two states there are many levels of polishing and note refinement. (Search the forum for “IMF”)
The question I’m debating is whether I should make the plants in my mind garden stronger, clean them from weeds and then expand or should I dump more soil and seeds and weeds and hope for the best…
Now that I read the above sentence, I guess if I want results now, I should curate and clean up. If I’m not getting enough results—more curation.
If I don’t have anything to curate, maintain and develop, then I would need raw material and my vault will be a dumping ground for a while.
I guess if you make a folder called “dumping ground” or “inbox” you’ll be walking the middle way—you have your dumping ground, a place of contained chaos, and you have your curated notes outside of it.