For me, coding was always about actually being able to build my designs — providing turnkey solutions to clients from design all the way to a live website. As I mentioned in the article, I came from a background where that was a necessity so I learned it along side design right from the start. So my motivation for what is “enough” was simply keeping up with coding best practices so had the experience and confidence to code anything I wanted to design.
The answer to your question is so personal, because it depends on your context. Do you freelance or work as part of team of employees? Do you contract yourself out to larger agencies, or work directly with clients? Do you work with small business with no in-house resources, or do you work along side larger companies who may have their own dev team?
The right amount of coding knowledge to make you as valuable an asset as possible will vary greatly depending on who you’re working for, and with.
In the end, you can never know too much. You’ll never think “man I wish I knew less front-end code!”. If you’ve ever felt your processes, designs, deliverables, communication, or teamwork could have benefited from a greater knowledge of coding, then keep learning.