I think everybody likes to know. Including the kids. Not wanting to know, or saying it doesn't matter is like saying we're not going to keep score. As long as you play your best, it doesn't matter what the score is.
I know pitching velocity is different, but in a way it is the same. It is a competition between pitchers and it is a competition within a pitcher to better himself. Are there other important things? Of course. If you can throw 100mph, but no where near the strike zone, you won't be doing it long.
Not saying you should be out there every game measuring pitch speed, but doing it a couple of times a year to see how things are going is fine. If a dad wants to do that, so what? I'll agree a dad shouldn't be out there bugging the **** out of scouts or being a pain. But to get a reading a couple of times a year, I don't have a problem with that.
I know my son likes to hear that he has gone up 4mph in the last 6 months or whatever. It is a form of positive reinforcement. He has been lifting and doing band work over the last two months. Once the season starts, we would both love to get a reading to see if he has made any progress by doing all that.
Whether you use a Jugs or a Stalker to do this, I don't really think it matters.