MediaWiki skinning scares people, and for good reason: implementing a skin that is not very much like Vector typically breaks every extension and gadget ever. Changing Vector is also a bad idea for the same reason. Changing the skinning backend itself is like opening a portal to unspeakable horrors: the fabric of the wiki turns inside out, extensions merge into unusable chimeras, and the site navigation starts breeding with itself. It is, generally, not recommended to try.