As someone who has recently done a Nation Roleplay I can tell you for certain the more complexity you have the less of a crowd you'll have. The objective here is to have a good balance between mechanical complexity and traditional free-form roleplay.

As someone stated before this all depends on what you're looking for. I personally have mechanics in place to keep Mary-Sues and Powergamers in check because we've all been there that we have that one guy who wants to steamroll everyone with his seemingly invincible armies. A simple principle I adhere to is you keep the storytelling elements free from the mechanics as possible where mechanics are only there for policing players with nations going on power trips.

One thing I've toyed with recently is using mechanics to create a challenge to write a story around the results in a die roll of something hypothetical or planned. In NRP if roleplaying is the act of telling history of your setting then mechanics are those variables of fate that dictates the outcome of certain events in history. What you want is collaborative storytelling, not a game.