Ability to customise admin panel with themes

I realise that there are ways to hack the admin panel, but I think that a lot of people could really benefit with extra control.

I have found several plugins which customise the dashboard, but they all hide the original HTML elements and insert the replacement. There should be a way to override the output of various elements (header, left menu, footer, etc.)

I think that I am going to have to make changes to the core wp-admin files to get the dashboard working how my client requires it to. This is a shame because it makes upgrading to newer version of WordPress a lot more complicated.

Despite this, WordPress remains fantastic. Keep up the great work guys!