OTOH, unless roads bring significant benefits, that is (as David points
out) too expensive.
Roads were a way to move troops fast--for Rome, and us (that is why our
freeway system was built, BTW). They also turned out to be a great boon
for commerce. I suggest that cities on roads would be better markets
(add buy/sell items?), and that they would have a great effect on a CIV
level. Face it, a tower, or castle, even, adds less "civilization" than
a major road and the things that spring up along it.
I guess that for sake of ease, I support the idea that random events (and
winters!!) should damage structures of all sorts, requiring repairs... or
triggering a decline into a pile of rubble, not unlike the collapse of a
mine.
For a road, it just gets worse and worse, and then is no longer
effectively a road--the potholes, etc., become more trouble than going
overland.