Beckles-
The problem with Diner's Club for me isn't cost, it's cceptibility. If you have a lot of business T & E in the USA, maybe it works. But out in the regular retail world, the DC takers are few and far between. And overseas, forget it, again except for the high-end hotels, airlines, etc.
Too bad-I'd prefer a card that gets miles over to UA but if I can rarely use it, it ain't much help.