In areas such as decision making, we can distinguish between art and science in terms of the mechanism that we use for decision. In other words is it a calculated decision or something else?
I am not sure if art and science are getting closer now than in the past, and I think there are many levels to this comparison. For example, art can be used disseminate science to the public, and is used to create new representation of data that improves our understanding of theories. Science in turn leads to new developments that artists can use (e.g. new pigments, new mediums, broadening our reality.)
Fundamentally, both fields rely on creativity. Without creativity art would be dull (or possibly nonexistent) and science would not have breakthroughs. Concerning your second question, calculated decisions are made within both fields. Most artists spend a great amount of time planning their next piece, and making decisions regarding what to portray, what medium to use, what are the piece's goals, and so on. Obviously the same is true for scientists.
Both artists and scientists also employ their instincts when working. These instincts are developed over time and with personal experience. There is a theory of learning called perceptual learning. One idea of perceptual learning is to train people to make decisions quickly and with little calculation - in other words improve one’s instincts. Different people within the fields of art and science employ both calculated and perceptual-based decisions to different degrees. I am sure there are other theories out there that can be added to the way we make decisions, so the story continues..