Part of the issue, as understand it, is that Monarchy's gold benefits rise with population, so a 20-pop capital at turn 140 or so will yield 10 gold, and a later game 40-pop capital will yield 20 gold. Given map constraints, in most cases, even the most ardent Liberty city spammer (leaving aside Domination puppets) will be more or less done dropping cities and building roads by turn 140 or so. If the average connection distance between cities is 5 road segments, and the spammer has 8 cities, the road discount would yield 20 gold per turn, which seems to a bit more than it needs to be. If the Liberty player later takes Wagon Trains, are his roads free (a la the Inca)?
The main virtue, in my eyes, of an extra trade route is that the Liberty player can choose to use the TR to address Liberty's relative gold disadvantage (vs. Tradition), or its relative food/growth disadvantage, but not both. And it isn't "free" since they still have to build/buy a caravan or cargo ship.
EDIT: Vic's suggestion would address the free roads issue.
The main virtue, in my eyes, of an extra trade route is that the Liberty player can choose to use the TR to address Liberty's relative gold disadvantage (vs. Tradition), or its relative food/growth disadvantage, but not both. And it isn't "free" since they still have to build/buy a caravan or cargo ship.
EDIT: Vic's suggestion would address the free roads issue.