whilst we would all love to see more PP's in the game the dev team are busy on other things at the moment
One of the biggest challenges that they and ALL games companies has at the moment is Adobe deciding they are no longer going to support Flash from near year
As most of Plarium's games run on the flash engine I am sure you understand the priority is to investigate a different engine to run the game on, webgl is out as an option as they have already tried it and I am sure that everyone here on the forums remembers that this was not a success.
They have found a temporary workaround by the use of the Plarium gaming platform for the .com servers and the use of Facebook's Gameroom for the FB servers but even these aren't perfect.
There are many aspects of the game to explore, PvP, Coalition Clash, Elisians, etc as I am sure you are aware of, PP's are just one aspect, whilst I appreciate it seems to be your favourite aspect it is not the case for everyone (I am more of a PvP player for instance and dont really touch PP's) and Plarium have the impossible task of trying to keep everyone happy.
There have been extra levels added in the last 12 months (more than once if memory serves me right however I have been playing over 4 years now) and other extra enhancements and features.
Please be patient while they work their way through ALL the player base's requests etc, we are all paying customers in one way or another and we are all as important as each other.
I am sure there will be more levels added in future at some point but as I am sure you understand, the resolution of issues with the Flash Engine being discontinued are a priority otherwise there will be no Sparta for us all to enjoy at all :(