The 1950s and the 1980s really weren't so different from each other were they?
OK so there were more TVs per household in the 80s, and branded underwear had made an appearance. And plutonium was easier to come by in the 80s.
But the similarities! Marty was able to use his 80s coin in the 50s payphone. And hook up his video camera to a 50s television.
Think 30 years the other way (not the second film but actual reality) and he would have struggled a lot more! You can't even use a modern smart phone charger to charge a mobile from 10 years ago!