A good four player version would be great!
Well, Swazi Casino is on pagat's Casino page, under the variants. It's quite the interesting beast. Definitely ups the level of the game pretty substantially.
If it's two player, I'd like it to be a bit different. A lot of the fishing games on pagat seem to be the same game as Scopa just with different scoring cards.
There does seem to be a fairly narrow family of these games, as far as what's worth playing. Maybe someone will suggest something else, but in the meantime, have you looked at Koi-Koi? It's two player and has some fishing elements, so maybe it will be worth a try. You need a Hanafuda deck for it though, or something that can substitute.