Regarding the original intention, this guy...
...argues that Star Trek
's simple, smooth, often almost-featureles visual minimalism was an artistic choice
and not just a reflection of the show's low budget.
And he's got a point. Lot's of cheap shows cluttered up their sets and backdrops like crazy. The author makes some mistakes (overgeneralizations and absolute statements that in fact have several exceptions in the series), but overall he makes a good point.
This reminds me of an article in Voyage 16 (dated 7802) of the Star Trek Giant Poster Book
. It was titled "Lights... Cameras... STAR TREK" by Allan Asherman.