QUESTION:  What is the purpose of learning about Neptune's weather
 if we cannot colonize it?

ANSWER Jeffrey Hayes,  FOS Instrument Scientist at STScI on April 26, 1996:

Learning about the weather on other planets gives us insight into
how weather works under all sorts of different conditions -- How do
clouds form when not made of water vapour, or how do winds behave when
the atmosphere is at -150F?  We can't do these things here on Earth, so we
study them on other planets.  Also, if we can understand how the weather
works on other planets, we can get a better handle on understanding
our own atmosphere, and so better predict things like hurricanes and such.