Until recently, level 8 was the maximum level in Ingress, but now there are more levels. What are the benefits when you level after level 8? I think there aren't any higher resonators or bursters.
There are no higher resonators than 8 but if you get above level 8 you will get some benefits.
I found nice infographics about it here: https://plus.google.com/+Ingress/posts/hJdabxHHmYD