The renewal system you propose seems like a pretty good idea. Not sure you even need the increasing cost. Just making it a small fee would probably mean 98% of works would never get renewed after the first term. Perhaps add a rule that the author can renew for free if he's still alive.
It's basically how the US system worked prior to 1976, though the terms were 28 + 28 renewal. Most didn't renew because they didn't make enough money to make the renewal worth it.
