Consider this :
* They have the same strength as rocket artillery, which is available around the same time.
* They are single use, while rocket arty is unlimited use
* They cost 150 hammers, while rockets 425, meaning you can get an arty for every 2 missiles, especially when you factor in the cost of carriers. As soon as that arty attacks twice, even if it dies after, you got a better deal hammer wise. Every hit past the 3rd one is a bonus, for the whole game.
If you are making them because what you are attacking is not accessible to rockets (coastal city, etc), consider making bombers. They do more damage et 65, are even cheaper than rocket arty at 375, and it's a better use of a carrier that would be empty after your first guided missiles attack.
Consider also the experience aspect. By the time you get guided missiles, you have military academies and maybe the gate which means you get 3 promotions for all new units. A bomber with 3x 33% damage to units promotion has effectively double damage, meaning 130 damage. Compare that to a guided missile that does not get any experience or promotion and will only do 60 damage. You'r wasting at least 70%+ of your hammers in this way. And that's not even considering repeated attack from a unit that does not vanish, if you do, the amount of hammers you are wasting approach infinity the longer the game lasts.
Conclusion, it's a useless unit that does everything worse than another unit. There is no reason to make it, and i never saw anyone playing on immortal or deity who made guided missiles, ever.
They need a damage buff or a bonus vs a specific kind of unit or something to give them an edge like the ability to strike anywhere on the map, or at least xcom range. That last one is the one i prefer, it would make them useful to build when you are pushing far away lands and don't want to deal with the hassle of moving units all the way there. You'd waste hammers for convenience, which is a good trade off. That would make me use them in my games, actually.