Dixie has in fact appeared more than K. Rool and also represented the mainstream Donkey Kong series outside it's own series in games such as Mario Sports, Diddy Kong Racing, and almost Brawl (yes I know she was supposedly a duo mechanic, but you can still play as her like you can play as Nana).
Most wouldn't consider being playable in a game series more to be a plus, but in the case that it rivals a character's importance I would count this. Not to mention Dixie Kong starred in her very own game. She seems to be very popular in Japan as well and Kongs just seem like the more preffered characters in the Donkey Kong Country series. Granterd King K. Rool not being a Kong would bring diversity, but still. Even if K. Rool is the villian, she's just as iconic to the series if not slightly more.
"Dixie has in fact appeared more than K. Rool and also represented the mainstream Donkey Kong series outside it's own series in games such as Mario Sports, Diddy Kong Racing, and almost Brawl"
Only appeared once more, it seems, but beside the point. Being in more Spin-Off games (not even DK games, for the most part) makes her more important? I guess that's your opinion. Okay.
"Most wouldn't consider being playable in a game series more to be a plus"
This already says "opinion".
"but in the case that it rivals a character's importance I would count this."
Again, I don't consider Spin-Off games as valuable resources for "importance". Look at Mario Kart 7, for example (granted, it's the only obscure Mario Spin-Off roster that comes to mind).
"Not to mention Dixie Kong starred in her very own game."
False. She co-starred in a Donkey Kong game along with her cousin, Kiddie Kong.
"Even if K. Rool is the villian, she's just as iconic to the series if not slightly more."
Somehow, I wouldn't consider this factual.
Anyway, this is clearly an opinionated argument, and you think you can snicker at me for questioning it. Cute.