It's good to read your words again, and I've missed you on these forums. I do hope you are doing well and wish the best of health to you.
... And still thank you for the shopping spree...
Bill, as you know, I've also hung up the towel a number of years ago as well, 21, actually, although I have taken the "big chance" and have come out of the closet occasionally to prove to myself that I can still spar when I feel unjustifiably embarrassed by standing on the sidelines watching everyone else. Maybe, I thinks to myself, they should have "sparring for crips."
I've been on the receiving end of a number of injuries caused by the fist, both in karate and out. Been on the receiving end of a number of head shots which left visible scars as well as those in which discoloration and lumpen malformations were fleeting manifestations. A finger was once severed, although successfully reattached.
So I may be able to offer a little personal insight.
If a person wants to do it he has to take his lumps. Many young males, including myself before youth escaped from the clutches, need to have hard violent contact, at least the contact on someone else. It must be a rite-of-passage, meaning that there must be a primitive inbred signal that tells us we must do it. In doing so, law of averages, as well as Murphy’s law enters into the equation and dictates you will get hit and hurt.
I've attended several "senior-level" dojo in the past where once they know you’ve been hurt it seems that any and every senior blackbelt comes out of the woodwork with their own little secret story of serious and/or permanent injury caused by their years of involvement in their fighting art. There’s no escape from it – you’re going to get hurt badly at least once; if you haven’t yet, it’s just because your number is still in the hat and you will be called.
Now my short answer to your question, Bill, is that hevy sparring is absolutely necessary, even if it's for only a few years because if you take the fierceness out of the fight you can never put the fierceness of the fight into the student. Guaranteed there are thosw who can fight and fight good without the karate, I know I could, but the mainstream of people can't even punch without pugilistic practice. Hard sparring, even if only for a limited time, will put people on the doorstep of being able to defend himself by helping to develop the ability to do the right thing under the pressure of the scare of getting hurt.
I remember the very first time I karate-sparred. It was my luck [what luck?"] I was matched up with a particularly aggressive brown belt. The word "Hajime!" pressed my osh!t button and I remember thinking "what do I do now to keep this guy from nailing me?" If nothing more I my fist sparring session was a great confidence builder although I already had no problem in that area outside the dojo.
So from the paths I have taken, what you are asking should be mandatory. It's up to the student, himself, how much of it he should immerse himself in unless you want a fighters-only dojo. It's also up to the student to decide when he wants no more breaking, cracking, bruising, etc. because we all have our limits and we all, sooner or later, get tired of the head banging, for one reason or another. If forced to , compelled to, coerced into, extorted to do so, exploited into, etc. after our own time to personally throw in the towel has passed, we simply quit.
Always with an even keel.