"Having attended church together for six years, Alex and Amy were thick as thieves." As a creative writer, what benefit is there in removing the phrase "thick as thieves" and rewriting this sentence?

Avoiding the phrase "thick as thieves" means avoiding a cliché, which is a valuable creative writing skill because original language has more impact on readers than making them read phrases that they have read countless times before. Originality also sets writers' artistic voices apart.

In Toni Morrison's Sula, why does Nel compare her mother to "custard?"

Nel uses the word "custard" to describe her mother's submissive behavior. This occurs after Nel sees her mother get humiliated without defending herself. Disapproving of what she perceives as her mother's emotional weakness, Nel vows to be strong, unlike "custard."

What is another word for "effusive?"

Another word for "effusive" is "enthusiastic."