There's a thingy called 'WikEd' - it adds a more functional editor with code highlighting, easier adding of some code the old bar fails at, find and replace, automatic fixes for various things, previewing without reloading, improved edit differences thing (also can be viewed for the edit you're making, again live), redo/undo buttons, sorting, case toggle, etc. I think it might be useful to install it for the whole wiki to use. Now, after doing this, the user would still have to turn it on by clicking an icon at the top right of the screen, next to 'log out', so it wouldn't force it on people if they don't like it.
To try it out for yourself, copy what's at my monobook.js to yours. To implement it sitewide, we'd copy it to mediawiki:monobook.js. Note that it doesn't work with any other skin, monaco being the only other one I think people here might use.GP