I like the imperial roads idea. But why do you have it as an event? Why not have it as a tech, available after construction? After you have researched it, 1-3 stone resources are placed (dependent on the number of cities you control) on the map within your borders. When you have connected the stone, the worker spell "Build Imperial Roads" appears in cities other than the capital, as per your rules.
How about this? Much simpler, in my opinion.
On another note, what about having a national wonder that gives you a spell, only usable in the city it is built in, called "Cause event" or somesuch, that can be used once per turn by a unit in the city. Whe used, a list pops up and you can choose to trigger one of the events by paying some money, sacrificing units, causing unhappiness or you name it. Entries may include "Library of Alexandria " (One time event, pay gold to rename the library to this name. It gives you 7 bonus beakers for as long as you have exactly seven units stationed in the city), "Perilous Research" (must have a laboratory in the city, loose the laboratory, gain a big research boost), "Polymorph" (pay 100 gold to cause one random unit stationed in the city to be sacrificed, replaced by a random unit from among all units in the game (not counting heroes) from all civs), "Fruitcake Elemental" (onetime event, pay gold to summon an elemental guardian. It is held, have strenght 7 and will deal 7 damage every turn to another random unit stationed in the city)... The list goes on!