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Some of the metaphors associated with the up-down axis play an important role in the extension of meaning generally, not just in the domain of the preposition. They include:
(a) Status. We talk of 'high' and 'low' status, and to achieve higher status is to go 'up' in the world, while to lose status is to go 'down' in the world; compare also look up to someone and look down on someone, or put someone down ("make someone feel inadequate/unimportant").
(b) Size. Up and down are used in various expressions indicating respectively increase and decrease in size: blow up a balloon, fatten up cattle, scale up a map, let down a tyre, scale down a map. Compare again high and low in high/low prices, high/low achievement.
(c) Degree of activity or intensity. Again up correlates with 'high' degree and down with 'low' degree: compare wake up, liven up, brighten up, cheer up, speed up, start up, pep up, perk up, wind up, keyed up, tense up, psych up, with calm down, slow down, shut down, settle down, quieten down, get someone down.