I practice N. Shaolin and I've been in it for five years. My style is a northern style and that's why I'm here. I've heard excellent things about the Wah Lum school over the years. It has an outstanding reputation. I agree with some of the above comments about high kicks. High kicks are not often useful in a fight. But let me say some words about how and when they could be used. In my view the only time they could be used is from outside gate. If you are at inside gate you should not try them. An opponent will just punch you repeatedly. The other problem is the opponent rushes forward as you kick. This is called jamming. It's a basic and effective tactic. Your kick impacts the opponent but their is no power because he is closer to you now than when you launched the kick. Jamming also works against punches. But it's easier to keep attacking with punches than with kicks for obvious reasons. Your balance is compromised with kicks and you can end up on the ground if the guy crashes into you.

High kicks are one thing, and jumping kicks are another. High kicks make sense as a training tool as they make low kicks more powerful. Jumping kicks could be used in combat where high kicks would fail. Jumping kicks combined with bridging motions(arm controlling) could take someone out, but again only from outside gate. I would say that a jump kick should be combined with a bridging motion every time. If you're at outside gate that prevents a lot of counterattacks from the other guy.

Real fights happen in close. That's why it's easier to jump kick high or kick low than to kick at waist level(groin included). Try it. If you are up close to an opponent the jump kick allows a high kick and it's an evasive move at the same time. As long as you include something to grab/check an arm with as you go up. I repeat that I would only do this from outside gate. And the way to get to outside get is to engage the opponent while stepping. You can't just try to walk around the guy. You'll never succeed without having arm contact first. If you get that then you slip outside and employ a jump kick. I wouldn't try this too often but I think it could work.

I'm not an experienced fighter(street) but I've been there. I will admit that I've never tried a jump kick in a real fight. I'm just reasoning with you as to how it could work. I think one problem is that people who can jump kick often don't realize the importance of controlling the opponents arms. They act like kickboxers and they get stomped when the other guy just rushes them. I also agree that all fighting is in-fighting, but that doesn't exlude the possibility of a jump kick. In fact it makes bridging motions more important. There are too many people in northern styles who think that they way to move around is to just use footwork. No way. You have to go at him, tie up arms, and then step to outside gate while remaing close. You have to keep contact with someone(arm to arm) if you want to anticipate and stop what they're trying to do.

Touranments are the other problem. People become convinced of myths about different ranges. You can't stand back in a real fight because there is nothing to prevent the guy from rushing you. So you have to adapt any technique(including jump kicks) to in-fighting. That's why forms are so important! They contain these arm checking movements and bridging techniques that allow you to get to outside gate. If you don't see that then you won't get the point of northern styles. Northern styles fight at the same range everyone else does: street fighting/in-fighting range. they just approach combat differently.
A lot of knife hand and palm strikes(as well as sweeps and kicks) work nicely in outside gate. But first you have to be able to get there. And you have to understand that you'll still be fighting in close no matter what style you do. Don't confuse sport with street.