Heh, that's weird because I'm the exact opposite. I grew up post-Crisis, and always knew the Kents to be alive outside of the movie where Jonathan had died. So I grew to like the idea of them alive and I remember when Lois & Clark came out I was so glad they opted to have them alive instead of Jonathan dead. But as time went on and I learned more about pre-Crisis materials, I began to appreciate what they brought to the character in spirit more than I liked what they brought by literally being there.

But I agree that the change was likely largely due to the omission of Superboy. Without that there was no outlet for them reguarly outside of adult Clark's flashbacks. Frankly I think that would have been enough but they went in another direction at the time. But really with all this time and reflection I think they had it right pre-Crisis. Superboy you have to tinker with to make it work in a more "realistic", less campy history of course, but all of it just crafted the better lore to me.