As some people have strong feelings about the look of the new skin, there is a way to change it for your own view. The Terms of Service disallow Administrators of individual wikis to remove/alter/hide parts of the new look (to keep the look consistent throughout Wikia). However, you on a user level can make whatever changes you like.
Each user has a Cascading Style Sheet (CSS) file that gets applied as a final tweak to whatever skin you're on. Those CSS files are editable wiki articles, just like any other on Wikia. For more information on User Styles in general, see this article.
The CSS file for the new look is Special:Mypage/wikia.css. Clicking that link will take you to your custom CSS file for the Community central wiki (If you want to have your changes apply to all wikis, rather than just one, go to Special:MyPage/global.css (thanks Xd1358!)).
Now, edit that file, and add whichever code snippet(s) you want, and save changes. Then do a hard refresh on your browser and you should see your changes.
Admins of wikis, if your particular content doesn't work well with the 550px space, and could use an extra 300px, you link your visitors here with a suggestion to implement these changes, if you can't or don't want to change your content.
Hide right bar entirely[]
This will hide the right bar, and allow the center content to take up the missing space.
#WikiaRail { display: none; } /* Hide right sidebar */
#WikiaMainContent { width:inherit; } /* Allow content to take up that space */
Put the sidebar at the bottom[]
This puts the sidebar content after the article, which still gives you access to the sidebar modules, though they're now wider than they originally are, so look a little strange, but are there at the way bottom if you need them.
#WikiaMainContent { width:inherit; float:none; } /* Allow content to be full-width */
#WikiaRail { width:inherit; float:none; } /* Jump sidebar to bottom */
#WikiaRail form, #WikiaRail section { width:95%; } /* Shrink sub-sections to fit */
Just hide individual sidebar elements[]
Pick the individual line(s) for the elements you want to have disappear.
#WikiaSearch { display:none; } /* Wiki search bar */
.WikiaPagesOnWikiModule { display:none; } /* Number of pages and Create a Page */
.WikiaActivityModule { display:none; } /* Recent Activity */
.LatestPhotosModule { display:none; } /* Latest Photos */
.WikiaBlogListingBox { display:none; } /* Popular Blog Posts */
#WikiaSpotlightsModule { display:none !important; } /* Sidebar Spotlights */
#WikiaFooter section { display:none; } /* Spotlights on the bottom */