There will be replies from those who know considerably more than myself, as I am no authority, but I'll chime in from what I know.
From anything I've ever heard from any viable source, high spinning kicks never had a place on the battlefield. That's not what they were designed to do. Certainly,like everyone else, I've heard such things, but never from any source that could be substantiated. They were conceived for contact sport and demonstrations, nothing more. I could be wrong, but I've never seen any substantial proof to the contrary. If anyone can offer proof, I'm all ears. My opinion isn't set in stone, only based on what I've read from reputable sources. Not hear-say.
That being the case, first, there is no such thing as an impractical kick. Any kick that is used in the wrong circumstance or at the wrong time is an impractical kick. Any kick that surprises your opponent and scores is very practical. By impractical I can only assume you are referring to the fact that they take so long to develop as opposed to say, a mid-section roundhouse. True. They don't generally work well when your opponent is fully ready. They do however, work VERY well once your opponent is commited to an action or is off guard or balance. It's all in the timing. Because they take longer to execute, you have to be able to time your opponent farther out. More difficult? Absolutely. Impractical? Not if you know what you're doing.
Regards,