I keep seeing some of these in the Pawn Shop and in Apocalyptic, but have no idea whether to buy them or not. Are the regular ones worth it or should I just keep an eye out for special ones?

I suggest you keep the shop search (located under the "commerce" tab) open in another tab in your browser to check the prices in the shop vs what they're going for in user shops. ^^

Many elixirs aren't really worth buying to resell but checking the shop search is the best way to check!

That's pretty much what I've been doing, though have been using Subetalodge to check, especially where multiple items of a particular type are concerned, like t-shirts or plushies etc. Thanks for the reply! ^_^