I don't have them in separate files but I can split them into that. However, some icons are multi part with variable transparency so that you'd have to get from the game directly.
Game text is a bit all over the place, unfortunately, and you won't be able to extract it that easily because I don't use XNA's default pipeline for anything but sound and graphics I think.
Btw, how much does Wikia actually help with creating content/layouts? I have MediaWiki installed on my site if you guys would rather work with that.
Huh. I guess that explains why I was able to export only PNG files from Underrail's XNBs.
My opinion is probably heavily biased, but Wikia isn't any better than mediawiki. Its wiki syntax should be identical, so simply copypasting content from wikia to a mediawiki even at a later point won't be a problem.
There are some ready-to-use videogame-related infobox templates in wikia. We'll have to edit them in any case to fit our needs. That's all, as far as I know. I don't have much experience in getting a new wiki started from ground up, though.
Layout-wise, no idea. I use MonoBook(mediawiki's default skin) instead of Wikia's default layout when editing so I don't even know what it looks like for the average user... T_T
Personally, I think it would be the best if you ran your own mediawiki and set it to use modified version of your site's stylesheet as default skin. Wiki editors shouldn't be concerned with the CSS, but rather with adding, organizing and updating content.
Oh, and wikia's WYSIWYG editors seems to add a lot of HTML to the pages. That might discourage editors used to wiki syntax only.
Just my 0.02