Consistency is generally good, but in this particular case, I _depend_ on this inconsistency in order to produce fresh values for theories on mutable structures (stacks, etc).  This change as written is going to make correct Theories incorrect, in the name of consistency; I'm not ready to make that trade-off.

Sorry to come to this conclusion late.  I think the next step is to separate out the boxing/unboxing parts, which shouldn't hurt any existing tests, and then tackle the other proposals here.

Thoughts.