I think u shouldn`t make the units too stong, because fighting whit big armies is beautiful and realistic, as long as it is controlable ( grouping soldiers really helps ) There should be at least one way to gain a resource without runnig out of it (for example trading in Age of Empires/Kings/Mythologie) because it really sucks to run out of resources. Unexhaustable farms can be good thing, because it is really annoying if you are at war and your reset farm qeue (AOK) is empty .