... is it more insane to try to stabilize a brick foundation, break up a concrete floor, and dig down... Or to levitate the house as if one was going to relocate it, and build the foundation upward (or pour a new foundation in place under it)?
No, I don't think I'm serious about either. Headroom is about 6' in the 1890's section of the basement (probably originally dirt-floor cellar?) but I'm 5'8" so that isn't intolerable. But every now and then I wonder what it would take to change that.
(Given that I'm within the hundred-year-flood zone I suspect the bias might be toward going up, but I'd be really interested in knowing just how bad either would be.)
Footnote: one website claims "The cost of moving a house starts at about $12 to $16 per square foot but can quickly rise if the home is heavier, bigger or has farther to go." So figure the levitation alone at around $20k. That's actually not completely unreasonable, especially if one wanted to do all the "ideal" ground-water, insulation, and radon measures and bundled them into the cost of the new foundation.