Make inhib turrets AND inhibs rapidly regen health
When out of "combat." This way they're actually an objective and not something that can just be whittled down and taken over 5 minutes.
And maybe make all of the regular turrets slowly regen health. If I've been successfully defending this turret for 10 minutes, I don't want to be punished for having it be taken because it was already half health from 20 minutes ago.
At the moment turrets are too easy to take down, true, but maybe what we need to do is let them REPAIR over time if they haven't been destroyed. The farther they are from the nexus, the slower they regen.
Now, I have another proposal that sounds crazy that isn't part of my previous one. What if for the outer turrets we had a new type of creep that goes out after 10 minutes into the game and begins to "repair" turrets, healing them faster. Or maybe even make it so that these minions can rebuild destroyed turrets? It would be interesting to see something like this play out, and it would counter a lot of the snowballing that is going on.