Covering it with tiles isn't a solution to not having to increase work on the finish, UK SSNs - the T boats definitely have them, not sure about S boats - are covered with those tiles because they reduce the subs acoustic signiture (and I read somewhere it causes less resistance with the water so it's more efficient - but not sure), the fact that it pretty much waves a magic wand over the hull is pretty much a byproduct of having to put them on.
I'm not sure if sanding/grinding would increase the speed, IIRC the tiles are put on with black putty-like stuff in the sort of "gun" you use to seal windows and the like. But one thing I have learnt is that sanding/grinding a weld down apparently weakens the weld so imagine that all the way around the hull in rough seas. Massive tragedy waiting to happen.
They are very different, that much i'm sure of. I recall a video of 2 Astute hull sections being "put" together but the crane could only get the sections to ~1 inch, from my very limited experience with welding that's a huuuuuuge gap for welding.
I'm in a Computing lecture at the minute, i'll have an in depth read later, thanks