Your dad scenario doesn't mention that the dads (who are big kids, most are anyway) get as much enjoyment as anybody out of this type of purchase. He will probably spend a little more as a result.
We love our children and sometimes we have to buy things that do not strike a chord with us. Begrudging indulgence that we parents believe will be karmicly repaid. The Ipod or Playstation comes out of the "community chest" so less for 1/72nd scale figures for big kid dad.
The slightest inkling that offspring are remotely interested in this hobby of ours should be rewarded by the kind of over weaning normally bestowed on child prodigies or baby pageant beauty queens.
I suppose what I am saying is don't skimp on your sons' or daughters' hobbies if they happily coincide with yours, it won't last so give him/her that bit extra. They deserve it for such intelligence and discernment.
Psst-when they grow out of it you get the figures anyway and these escape wifey's attention or alimony (I think is what it is called in the US). A good argument btw for kids to use with dads who are reluctant to part with their money. The Alimony Ploy is a good gambit but the timing has to be good and not to be used if mom and dad still hold hands or wear matching clothes or say "I love you" more than once a year.
In the end adults are likely to be customers or purchasers of the big box whether it is for a kid or not. The info and appeal of the box has got to be a big factor affecting sales.