I like to bias the amount of practise in certain attacks to the frequency with which people tend to be attacked in that manner. In my experience I have never been attacked by a kick, and have only ever seen one other person kicked, and thats when they were on the floor. Admittedly I do know of people that have been kicked, but only good martial artists tend to try this, and in my opinion these type of people are less likely to start fights.
Also, ideally you don't give your opponent a chance to kick you (getting inside and unbalancing them before they attack). Hands, elbows, grabs are much harder to stop my moving in to closer range. i.e. I would expect most kicks to be when you expect an attack (i.e. a face of like scenario) where you can quickly stop the kick occuring.
HOWEVER, I do think its useful training against kicks (though I only know about 4 or 5 defences purely against the kicking foot; obviously you can do stuff like irimi-nage). I think its best to be prepared for every eventuality.
N.B. also non-martial artists often have a problem producing convincing kicks - thats why I think we should have more striking & kicking as part of aiki practise.