You are correct that you shouldn't have to clean the contacts each time. Roombas charge through the electrical contacts on the base station and Roomba, passing electricity from your wall to a battery on the Roomba. From your post it doesn't sound like a base station or battery issue.
We need to diagnose the root cause. It sounds like it's not a contact issue since you've been cleaning them regularly. Check your base station contacts as well.
Is your floor uneven? You shouldn't have to wedge something under the Roomba. If you pick up the Roomba and place it on the base station, does it charge? To me so far it sounds like an issue with the Roomba correctly emplacing on the base station. I would try a different location for the base station to see if that rectifies the issue. If not we can continue diagnosing.