I agree with more customizable property inputs.
Also check this: Add free text input for box-shadow property
It would be awesome if all “complex” properties (using combinations of values, optional values, etc.) had a toggle to switch to free text input.
Like you said, it would allow to keep things clean and simple for basic use, but it would also provide a way to be totally free and use shortcuts (like x and y values instead of top, right, bottom, left), CSS variables, or who knows?.. maybe dynamic fields {}?