I remain completely persuaded by the organic road concept. The objections to it are terrible ideas.
"I should have control over everything." Have fun micromanaging which foot your armies lead with when they start marching.
"Military units can build roads." All the trouble of using a worker, plus you tie up your soldiers doing worker stuff.
"Basic roads can be organic, but advanced roads should be built." Reducing organic roads to being primarily a cosmetic representation of trade, with "real" roads having road problems that organic roads are an attempt to avoid.
"The Romans built roads." The Romans had wooden spoons too, but nobody's proposing gameplay about it.
"I need to control roads because they're tactically important." There will be other ways to move fast. Haste spells, gate spells, magic carpets, forestwalking, plain old cavalry.
"There should be many manually-controlled graduations of road capability." Great, now roads are a major expenditure and building and customizing them is a large part of playing the game. What is this, Elemental: Railroad Tycoon?
"Manual roads will be optional, so they should definitely go in." If manual roads go in, they'll have a design influence over everything associated with roads. Magical travel options may be neglected, as may ways to build an army for mobility. Movement speeds and trade revenues will be balanced with the knowledge that there are manual roads, making organic roads less important than they ought to be. If roads have a cost in labor, resources, money, etc., that cost will be figured into the system for those things (e.g., towns should produce X gold, but if roads are in, towns should produce X+Y gold so that the player can spend Y on manual roads). Optional or not, manual roads should be excluded.
One wrinkle I want to add to organic roads: the road network should use existing roads where possible. A new connection shouldn't develop a road in a straight line from A to B if there's an existing road it could tie into instead.
I do think roads are a liability sometimes. Generally, in games with roads the enemy can use the roads you build, and the reinforcement corridor from your capital to the front lines is also a highway for invasion if the enemy can get to it. Roads also let the enemy know where your points of interest are -- follow road, discover city.
But these liabilities are good. As roads flourish in the endgame, they'll be a modest nudge toward conclusive engagements. There won't be hidden capitals that you have to hunt all over the map to find. And on the defensive, rather than security by obscurity, you'll have to confront the enemy to win, whether it's with magic, diplomacy, or your army. A common complaint in games like this is that the endgame bogs down. In addition to their other advantages, organic roads will help focus the endgame.