well i agree it looks good as a ugc case and I think its cool what xelement5x did there, but I'm not sure if its worth doing because some of the later games didn't even come with jewel cases, plus theres the cd/duo games that are cd's anyways. Also if you buy any games used, half the time they only have the game. And many of the original cases are damaged (faded spines, scratched or cracked covers) there's plenty of room in a dvd case for the game and the manual.
Recently I was also thinking of some nicer ways to put them in the dvd case by using collector card plastic sleeves which are pretty much the same size as the original sleeve. could glue them in or glue them to a piece of thick paper the size of an insert and then put the manual behind that perhaps.