Looking through the various theme files, some files build a string which is later rendered, while others echo the content directly. It would be nice if a consistent method was used throughout all theme files. I'm not sure how much re-programming that would entail, and how much it would mess with existing extensions.

Here's my secret motivation: I like it when the theme file builds a string, rather than echo directly. That way, extensions can use str_replace() and other string functions to insert, replace, or otherwise manipulate the content without the need for an explicit delegate.