[Rupert]

You can't just drop bombs on targets on the ground from orbit - you need to deorbit them, and unless they have a fair bit of delta-vee (i.e. they're a missile), you you do, they'll be doing it slowly (by aerobraking over several/many orbits) and thus will be horribly inaccurate.

As far ramming with nukes - you won't get them to all go off properly because some will vaporise the rest - you'll get a lot of fratricide.