Is "University Challenge" right that this is a gerund?

Riches are for spending.

I take "spending" as a verb here (cf. "riches are to spend"). Syntactically, there are several indications that it's behaving as a verb:

[1] it can be modified by an adverb: "Riches are for spending extravagantly/cautiously/recklessly", whereas nouns cannot (normally) be modified by adverbs.

[2] Unlike nouns, it has no plural form - we can't say *"Riches are for spendings".

[3] It can take a to PP complement: "Riches are for spending on luxuries".

Traditional grammar analyses "spending" here as a gerund simply because it is complement of a preposition, i.e. a location where nouns normally hang out. Which doesn't tell us what part of speech it actually is -- a typical weakness of traditional grammar.