I think you are right. I am on level 60 with no bonus items and it does seem impossible to advance any further without a lot of luck. It's not even possible to go back a few levels and try and get to level 60 again with a bonus or two. The only option seems to be to start the game again.
When I got stuck on one of the earlier levels without a bonus, it was possible to go back to the start of the 'epoch' I was on, but that is not available now that I am on 'epoch' 3.
Is that part of the game or a glitch, I wonder?