1) Theme installation system:
Great plan to add an easy possibility to change the Moodle page look. An easy installation system like the language packs might not be convenient with the actual theme system. Themes contain XHTML, CSS and PHP code. You know what may happen when anybody can include any PHP code to your application.
I have been thinking about a possibility for some time now every once in a while - without a solution.
One possible approach might be to split themes into a base theme with the PHP/XHTML part. This base theme is securely checked and installed by administrators. And a CSS part which may belong to any base theme and is installed like languages.
2) The theme competition:
A competition might be a good way to communicate how attractive Moodle is or may get for theme designers.
The base for this attraction is a truly clean XHTML structure without inline styles and without depreciated HTML properties for page layout. To reach this goal the competition might be a valuable challenge for all Moodle developers to clean up the code and replace all inline styles and all HTML attributes with CSS for Moodle 2.0. This process is already on a good way but actually much too slow to be finished for 2.0.
3) Martin, you'r not fair with the maintainers of the existing themes when you just call their work crappy. They invest a valuable amount of work to maintain the themes and update them for every new Moodle version. And they have helped Moodle getting to the point it is today.
4) And there are reasons why Moodle is not as attractive for theme designers as other systems are. As a good base for themes you need a consistent XHTML code base with sufficient CSS hooks. On this base good themes will spread up.
Creating a functional and good looking theme is much work. When this work is done you need to start creating Moodle specific corrections for many areas - modules, blocks etc. to get them looking consistent. Some modules or resources you even can't design - that breaks the value of a theme designer's work.
And you may think about the Moodle developer support strategy for theme designers with their special interface oriented needs.
Lets create the split, easy install theme system and let's clean up Moodle code for a marvellous base for a successful theme competition!