I did answer most of the questions in your post before the above, with the exception of if it had worked before....and I don't know because this was the first time I tried the "display only" attribute.

I know some of the stylesheets are for mods, like the lightbox and un_classic (for the wishlist mod). But I think I do remember trying to delete the stylesheet-old.css and it causing problems with my site. So is anything in that dir autoloading? I thought naming it -old will not let it load.

So, port/update whatever is in the -old stylesheet to stylesheet.css and then delete stylesheet-old.css?