(Yes, some of these could have appeared under "friends," but I was trying to keep each entry at a more or less equivalent length, and in any case, they're all kind of more tangential.)
Vacation Van Honk
VACATION VAN HONK IN THE HOUSE! The Honkster! Double-V to the H!
Yeah, I got nothin.' I do think it's interesting to see this guy just sort of appear now and then, a remnant of some sort of idea the producers had that never went anywhere. Like the weird crap that sometimes shows up in the code for videogames that never actually makes any in-game appearance.
I know Donald originally wore a sailor suit 'cause that's what kids did, and he was conceived as a mischievous child, more or less, but it's interesting to see the show try to make sense of it. Grimitz, his commanding officer, doesn't get a huge amount of screentime, but he's an entertainingly Strangelovian character, and the part where Cinnamon Teal hypnotizes him is funny.
Fenton's awesome, and his mom's awesome, too? Must be genetic. I seriously did not have high hopes for the character when she first appeared, but she quickly endeared herself to me, thanks to great voice acting and a few cool starring-ish roles. I still wouldn't mind a hint as to what happened to Fenton's father, though--literally all we know is that he called her "useless," which suggests that she may be sublimating something with her constant TV-watching, but more than that--who can say? Only bad fan fiction can save us now!
Fenton's girlfriend wasn't really conceived as a character at first, so much as an aspiration. She bore exactly the same relationship to him as "a better job" did. Later, however, she comes into her own a bit, with her crowning achievement being her robot-operation in "The Duck Who Knew too Much." I woulda loved to see her have more opportunities to do cool stuff.
I like the fact that her relationship with Fenton seems more or less stable (in contrast to Donald and Daisy); I would've liked to see a bit more of it, though.
Oh, Dijon...debates over his exact ethnicity notwithstanding, you have to admit that it's not exactly a racially sensitive depiction. It really is odd the way Ducktales was able to get away with things that comics at the time never would've. I am on the record as noting that my opinion of him softened a bit during "The Golden Goose;" maybe if the show had kept going, they could've made him even better. Then again, if it's true, as Christopher posits, that "Attack of the Metal Mites" was made after "The Golden Goose"…maybe not.