Possibly rewalling could replace stone detailing. If you think about it, this would work like so: you to cut out the section of cavern you'd like, leaving rough edges (pickmarks, etc.). Then your mason constructs a certain amount of brick-like objects, or maybe just rock blocks. These are then used to construct a basic wall. Or, if you have more time on your hands, or want to make something extra-special for that whiny noble, you have a further step - the mason takes the stone blocks or bricks and improves them somehow (I'm not really sure what the word I'm looking for here is) by engraving them, or making them all the same size, or what have you.
This would mean that to make a mid-level wall in a 3x3 room, you'd do the following:
XXXXXXXXX
XXX...XXX
XX.....XX
XX....... First mine out the section
XX.....XX
XXX...XXX
XXXXXXXXX
X=unmined rock
.=rough floor
XXXXXXXXX
XXXOOOXXX
XXO...OXX
XXO...... Then build up the walls
XXO...OXX
XXXOOOXXX
XXXXXXXXX
O=basic wall
Of course, for floors, you'd need to get some kind of block placement, perhaps building a channel and then putting a block in it... I don't know, something along those lines.
In regards to the sewers ideas, maybe, if it's at all possible to do, it could make both adventure and dwarf mode a lot more versatile. Instead of just building a well, maybe you could build a reservoir of sorts by making a 'pipe' to the underground river and leaving the pool open - requiring more work than a well, but allowing a larger number of dwarves to drink. Likewise, how cool would it be to infiltrate a kobold fortress by swimming through the sewer system?