This word is really hard to explain due to subjective feelings and all sorts of flexible translations. Here is my gross summary:

• 1) No.1 rule: If the adjective is negated by 不, then 很 is not a filler. Indivisible adjectives which begin with the character 不 are exceptions.

• 2) If the adjective ends a “(X is) Y” declaration: filler, “very, really” or in-between ;)

  e.g. 她很漂亮。她的回答很好。很好。大厦很高。

• 3) If the adjective ends a “(Is X) Y?” question: “very, really”

  e.g. 她很漂亮吗？她很漂亮？她的回答很好吗？很好吗？

• 4) If the adjective becomes a modifier preceding a word: “very, really”.

  e.g. 她是个很漂亮的女人。那个很漂亮的女人是她。她很好地完成了工作。

• 5) Otherwise, 很 is probably not a filler.

It can obscure the lines if we simply want to show that the object is obviously happy, pleasingly beautiful, displeasingly expensive, etc. Polite remarks also do. To me the filler is not pure or the semantic of the sentence structure “subject(+很)+adj.” is not that simple. For example, “那面墙很白。” never means the wall is simply “colored white” but “conspicuously white at first glance (not necessarily snow-white)”. To simply emphasize the color type, people would, for instance, say “那里有一面白色的墙 (there is a white wall; not 很白的墙)” and “那面墙是白色的 (the wall is colored white; not 是很白的)”. So, it is confusing that both 那面墙很白 and 那面墙是白色的 can be translated to “the wall is white” but the nuance is not neglectable sometimes.