After 30 years of daily inserting my key into the door lock and ignition lock, both are worn out and jamming, preventing the key turning, even with wiggling the key. The pins are worn out since the locks even give trouble with my original Volvo spare key which is in perfect condition as rarely used.

I cut up a lock at the bone yard to see how it works so rather than try to get a locksmith rebuild the locks with new "pins" (they are actually metal rectangles about 13mm by 6mm with holes cut in them at varying distances from the their edge) if such things are available, and cut a new key at big expense, I would like to just remove (drill out?) the pins if possible, so that the lock & key has no security function anymore, but just simply turns the lock. Is this doable? No one steals 30-year old Volvos where I live.

Anyone done this or is there some better method?

The door locks come apart reasonably easily. Not sure if 79s have the old style barrel or the newer clip on type. To get the clip on type apart you have to uncrimp the chrome face with the keyhole in it. I did this to rekey a lock awhile back.
The ignition lock is quite well armored and I have never been able to get one apart. It seems to me they "punch" in the housing to lock the barrel into it. I think you would have to drill out the "punches" to get it apart.

It would be much easier to get another set of locks from a junkyard car. Any locksmith should be able to make you a key for the set.