i could go either way.  possibly useful for E-J, but i agree it's a borderline case.

びっくりするほど	221980
ビックリするほど	102496
吃驚するほど	3769
びっくりするほどの	23728
GG5: びっくりするほど surprisingly; astonishingly; shockingly; stunningly; wonderfully; marvelously

My initial view too, but on looking I see it's very common, and there are examples all over the place (one Tanaka sentence). Probably we should accept it as something likely to be looked up by learners.

@@ -3,0 +4,3 @@
+<r_ele>
+<reb>びっくりするほど</reb>
+</r_ele>
@@ -8,0 +12 @@
+<pos>&adj-no;</pos>
@@ -9,0 +14,3 @@
+<gloss>stunningly</gloss>
+<gloss>astonishingly</gloss>
+<gloss>wonderfully</gloss>

I don't see a need for this. Meaning is clear from its parts.