using "the"+adj without a noun

In most European languages, Article + Adjective constructions can have specific reference; the German nickname for Chancellor Konrad Adenauer, for instance, was Der Alte, which translated literally as 'The Old One'.

While English speakers can and do often delete nouns and pronouns, in context:

• Q: Do you want the red one or the blue one? A: I'll take the red, thanks.

generally in English, constructions like that can only have Generic reference, not Specific:

• My great-uncle is the fat one in the middle. [Specific reference = 'the fat person']
• *My great-uncle is the fat in the middle. [ungrammatical with no head N to modify]
• My great-uncle is unfortunately among the fat. [Generic reference = 'fat people']

So, the coarse, the subtle, the ridiculous, the sublime, the stupid, the uneducated, all are fine, provided that they don't refer to individual contextually specific things or people, but rather generically, to all such things, without individuation.

What's interesting is whether they have to refer to classes of people, or of things. That's a matter of interpretation, and varies a lot with the adjective and the context.

That's fine, assuming by "the subtle" you mean "things which are subtle".

Compare with the phrase "from the ridiculous to the sublime".

Yes - this is an accepted form of usage. I'm fairly certain that it is used more when speaking in sweeping generalities as in your example "the coarse" and "the subtle."

This is not really less consise than the alternative "coarse thoughts" or "subtle thoughts."