https://www.edrdg.org/wiki/index.php/Editorial_policy#Part-Of-Speech_(POS)_Issues

Thanks. I've tweaked the editorial policy to reflect this.

gg5, luminous, wisdom
重要を	1,532	2.8%	
重要さを	52,991	97.2%	
---
の重要が	        584	5.5%	
の重要さが	10,018	94.5%

In meikyo it's 形動 only. We sometimes drop "n" if one or more of the kokugos has the word as 形動 only and its use as a noun is rare. I think it's OK to do here.

@@ -19 +18,0 @@
-<gloss>momentous</gloss>
@@ -20,0 +20,3 @@
+<gloss>significant</gloss>
+<gloss>major</gloss>
+<gloss>key</gloss>
@@ -22 +23,0 @@
-<gloss>major</gloss>

重要	29761919
重要な	11874488
重要が	3377
重要さ	112721
Daijr: （名・形動）[文]ナリ
Daijs: ［名・形動］

Although this is almost invariably an adjective, the kokugos (as usual) label it as a noun as well. That's part of the reason we have stuck with "adj-na,n".  I wouldn't really mind dropping the "n" in these cases but I'd like it to be generally agreed among editors and contributors that walking away from the "名・形動" is the best path.

See for example, 完ぺき [adj-n] and 完ぺきさ[n]
The noun is 重要さ, right?
重要さ	112721

sankoku:形動ダ

@@ -18 +17,0 @@
-<pos>&n;</pos>