By how much has imagination developed through NOT KNOWING about the Earth, the sea, the solar system, the universe etc. ?

Plenty of evidence suggests that without knowledge, imagination takes a turn for the worst and soon plunges into insalubrious fantasy and myth. This is particularly apparent when persons obviously lacking in knowledge of astronomy & space use their imaginations (or more correctly other people's imaginations) to conjure up "explanations".

Inigo Montoya: You keep using that word. I do not think it means what you think it means.

'ignorance' =/= 'imagination'.

That's an interesting question... without knowing what was beyond (or under) the ocean, Man invented dragons & sea monsters; Once discovering new lands, there were imagined creatures living on them... once the lands were conquered, and speculation about the planets arose, space monsters became the norm. 

I would guess we'd need to know *a little* about something to imagine things about it; the greater our horizons, the more imagination is needed to fill in what *might* be out there... 

I'm sure a lot of imagination. The Bible teaches that man can “never find out the work that the true God has made from start to finish.” (Ecclesiastes 3:11) Hence we will never know everything about God. The wisdom behind God’s ways is “beyond tracing out.” (Romans 11:33) However, God is willing to reveal his ways to those who want to please him.—Amos 3:7.