The specialization tree could be a nice addition.
Id say however it would come probably come down to simpler benefits more along the lines of choosing to specialise in defense, offense or economy. They just seem like broader areas that would fit a greater range of play styles.
Defense provides perks such as stronger walls and buildings at cheaper costs and would have a greater array of defensive options to construct.
Offense same applies for their units, higher stats and cheaper costs maybe faster production.
Economy could have increased resource yield and faster rates. maybe gain trade benefits or such.
Of course they would be fine tuned to suit each race's different strengths and weaknesses.
Thats' my 2 cents anyway.