Yes, there is a maximum EV, just like DV for every hex, in fact, both numbers are stored in exactly the same way in the database.
In game terms, the economic value of an empire is a factor upon how large, and how many ships will appear in the shipyard, ie. the ability of an empire to construct ships. So, if we think of it then purely in terms of construction capacity, a mission then constructs a shipyard or shipyard facility will increase the EV, and a mission such as a shipyard assault will decrease it, as both these missions can be thought of directly effecting the ability of an empire to construct ships.
This opens up the possibility to develop an entirely new economic model, if for example we take complete control of the shipyard via SQL, PHP, and a website. (I just lost half the audience here, I'm sure). Allow me to explain, by using phpscripts to access the SQL database directly, we can 'buy' and sell' ships through a website just as if we were buying them from the shipyard in the game. The advantages are that we can control exactly what is on offer, (an OOB if its desired), and also WHO gets them (eg you cant buy a Dread unless you're a Rear Admiral). The disadvantage is, that you have to log out of the game to buy your ship.