I like this question because it's challenging. Oxford Dictionary of English gives the example
She is more than happy to oblige.
For this structure (i.e. 'more than' + adjective), the dictionary places 'more than' in the adverb category and defines it as
extremely (used before an adjective conveying a positive feeling or attitude)
Now, my best surmise is that in your example 'more than' acts as an adverb too, and could be replaced with a word like 'utterly' without any significant change in meaning:
You'd think that would be utterly enough for most of us but meanings change and new words are being created all the time.
If so, 'enough' is the head of an adjective phrase, which functions as the complement.