Wish that was simply pasted to the top of every SEO forum.

The points made about structure are quite important and tend to be a natural part of disciplined coding.

There may be a more specific reason to make the effort. Google states that valid coding is not that vital, yet the pieces of data I've seen that relate to page load, size and crawlability tend to suggest otherwise. As mentioned earlier, good code may allow more of a page to be indexed but may also allow more pages to be indexed, within the same time frame. This can only benefit a site.