My hopes for Impa aren't as high as they used to be, mostly because my hopes for the Zelda series were dashed when I saw that Link had barely changed at all (aside from some extra poly's here and there, and better hair). That being said, Impa still has my full support as a Zelda character, if only because I can't stand the notion of many of the 'one-off' characters people desperately want in Smash - Ghirahim, Masked Link, Skull Kid (with Majora's Mask), Midna and various other assorted characters. Sure, these characters may rate higher on many polls, but I think it's safe to say that the fanbase doesn't always know what it really wants. Proof of that is how few people wanted Pokemon Trainer in Brawl - all sorts of ridiculous suggestions were made for Pokemon reps, but rarely Red - and yet he's turned out to be a key character in Brawl, and now that he's in Smash, I'm sure many of us can't help but think "he's so important to his series; why wasn't he here all along?".
And it's for that reason that I want Impa. And Tingle, for that matter - my ideal Zelda roster would be Link, Zelda (no transformation), Ganondorf/The Demon King, Impa and Tingle, as the five characters who have arguably been re-incarnated the most through Zelda's vast timeline. It's for this same reason that I'd prefer a character like Toad to a character like Geno, among other such choices. These are the characters that are truly influential to their respective series', and the ones who span generations of gamers. You could ask an old-school NES gamer, a new age Wii gamer and a gamer who jumped off the Nintendo ship after the N64 who Impa is, and chances are all three of them would know, which is something that can't be said for the likes of, say, Ghirahim.