the maintenance is marginal when you compare it to the original cost
If you think that marginal==none then you have some reading cromprehension problems.
Once you have a bunch of high capacity routers and fiberoptic channels, the costs get reduced to the utilities bill, a number of maintenance guys and sysops and a repair here and there, wich is a tiny cost if you compare to the cost of laying maybe thousands of miles of fiberoptic and buying those super-duper-powered routers.
Of course you have more costs when you have more bandwidth but the cost isn't that big compared to the instalation costs, and you can't tell me it's otherwise....
there had to be quite a few detonations to get the (small) craft moving anywhere at speed. A single blast won't do it.
now my quote from the wikipedia article on the machine you're talking about
The smallest 4000 ton model planned for ground launch from Jackass Flats, Nevada had each blast add 30 mph (50 km/h) to the craft's velocity.
If you call a 4000 spaceship small, i don't want to know what would be big for you.... As a side note, you're somewhat right, as the nukes had a built in reaction mass that "pushed" the ship. But the part about "blast chambers of precise dimensions" is a bit off too, a huge plain shield of a special material isn't a blast chamber and doesn't have precise dimensions at all (it just has to be huge enough to protect the ship).
E = MC ** 2 +- 3db