Dare I say that I think it may be a little plain for an emperor.
Bare in mind that Caesar had the Colosieum and all its grandeur.
However a town prefect or senator, a rich trader or foreign dignitary, even the owner of the gladiator school would have a suitable box for entertaining clients and visitors (some things never change it is the same today with corporate boxes at football).
Are you planning on doing more seating? If so what style ? How are you doing it?
A couple more boxes (maybe less grand) would look great, and a rack of benches for the paying plebs would also look great.
Actually does anyone know of some 28mm scale Roman spectators on the market? It might be a niche market but I can see a few arena builders will be looking to fill their stands.