Many people are happy with the instaroads because:
1) roads are free (only a tech requiered) and inmediate.
2) they are freed from building them.
And I suspect that the AI can't build roads. So insta-roads fixes both issues...
But I'd like to be able to build roads: MY ROADS. They would go the path I decide. Building them should have a cost of 5 or 10 gildar per piece. Mancers could build them for free, for that of "balancing". And the AI...should be teached to build them too