What does this だけ mean in particular?

Question

I read the definition of くだら◦ない【下らない】:

［連語］《動詞「くだる」の未然形＋打消しの助動詞「ない」》まじめに取り合うだけの価値がない。

I know everything but that だけ. I've searched it up but I have no clue "which" だけ is used here.

Answer 1

I am going to plagiarize my own answer here.:

Understanding the だけ in this context

I am not suggesting it as a duplicate because I will explain your phrase at the end.

Broadly speaking most of だけ's usages fall under two general categories: a negative sense and a positive one. I think because the negative sense is taught earlier to us Japanese learners, most people are more familiar with that sense. But the other meaning is also very common and unfortunately easily confusable with the negative sense.

The negative sense functions to limit a degree, scope, or reference, and is explained as:

1. 範囲を限定することを表す。「～ばかり」、「～のみ」。(Wiktionary Japanese)
   in a negative, limiting sense: only, just, limit (Wiktionary English)

But here the other sense is invoked in your text:

2. 分量・限度・程度を表す。「～ほど」、「～くらい」、「～かぎり」。
   in a positive, non-limiting sense: amount, as much as

As explained in that Wiktionary entry:

ある程度は肯定的に評価できることを表す。

• おんぼろの中古車だが、走るだけましかな。
• タイムはともかく、この悪天候下で完走しただけ立派だ。

So given that this is "as much as", 「ほど」 and 「くらい」 are synonyms that might be of help. まじめに取り合うだけの価値 means "as much value as being seriously considered"

まじめに取り合うだけの価値がない: not worthy of being seriously considered/not worthy of serious consideration/attention