As far as jumping kicks, well, as an opener, I think there is some merit to them, for those that can do them well and practice them in actual application. I prefer jumping knee strikes, because I like to be VERY close when sparring. If I can't elbow without moving my feet, I feel too far away! Are they a good go to/self-defense technique? I'd say probably not, at least not for the majority of us!
Can the spinning leg sweep (like a spinning hook kick, but done crouched to the ground) ever work?? That seems like the most useless kick to me. I have seen it done in martial arts practice, but never against an actual opponent.
One of the very few physical altercations I've has in my short life consisted of this, and nothing but this! It was a situation where, apparently the girl I was hanging out with on our local "celebrate how awesome our town is day", was the girlfriend of this guy with some angsty teenage possessiveness issues. Anyway, he came up to me, his buddies ringed around, and he proceeded to be all big n' scurry n' tuff. (Tricky to do, when your "second in command" is wearing plaid leggings and Hot Topic "combat boots"...) Anyway, it was a generally silly situation which scared the crap out of 15-16 year old me. While he was still posturing, I swept him. He fell hard, and I scampered back to the main street where the cops were. So, if you are ever encircled by angry 15 year olds who've probably never hit anything before, it may be a good option! Otherwise...
Oooh. Another useless flashy kick story as effective self-defense. Around the same age, I was at a local rock event called "homegrown." I think attendance for the whole day must have been MAXIMUM 200 people... Anyway, my group of friends somehow really angered another group of teens. Throughout the day, they become more and more threatening. Finally, one of my friends noticed that a bunch of them had sort of "mustered" and were heading across the field to where we were, looking kinda angry. He told me to do "fancy Karate stuff." I did a bunch of jump-spinning kicks in series, and tried to look super-cool about it. It worked, the scary guys stopped and turned around. Although we did end up having to book it for our car later that evening anyway...
So yeah, perhaps flashy kicks have some good uses as fight deterrents, when your would be aggressors are easily intimidated teenagers who are more interested in posturing than actually hitting you. Outside of that, I like my elbows, palms, and low kicks, thank you very much!