A unit only gets captured if it has defense 0. Attack 0 just means it can't capture cities (which is what you need), at least that's what I've heard about it.
IMO, defense 60 is a little extreme - this means that the unit will never get destroyed! Since a land-mine can't attack I think the cruise missile flag won't do anything.
I think a land mine unit should be very cheap (say 10 shields) and a rather low defense, such as 4-5, so that in modern times it only has a chance to damage offensive units, while destroying them only in very defensive terrain, like mountains or jungle.
I also think that smart weapons is unrealistically too late for a land mine. Land mines have been around at least since 1930's (maybe in WW1 as well, I'm not sure) and definitely in WW2. So my suggestion for prerequisite tech would be something like Mass Production.
A different suggestion is that you could possibly have more than one type of mines, with the same graphics, so that they evolve with type.
An early version, maybe, available with Mass Production, with defense 2-3, cost 10, so that cavalry which is common in that period has a chance against them.
A later version, maybe available with Minituarization, with defense 6-7 (so that they are effective against tanks), cost 20, and maybe more expensive (cost 40) anti-tank mines, with defense 9-10, available with Minituarization as well.
Hidden nationality is good, but it means that in peace time the minefields will have to be protected as the AI will try to destroy them!
The thing with paradropping is that you an airport in the city from which to airdrop mines. I don't know if it would work, but maybe giving mines a footsoldier flag, and introducing a unit like a truck (made by Dark Sheer) to transport 'footsoldiers' would solve the problem of laying minefields.
Another possible issue is that the AI might build lots of mine units to defend its cities (since they are so cheap). This might finally solve the problem that the AI keeps spearmen even when you have Modern Armour, but I'm not sure what effects it will have on game balance. Of course, heavily mined cities are quite realistic, but having an army practically fully comprised of land mines is not!
These are just my thoughts on the issue of land mines in Civ3.