They can be. For example multi-tape turing machines can be nice for modelling certain problems (e.g. "monotone turing machines", with a read-only tape, a write-only tape and a normal read/write tape appear a lot in algorithmic information theory).
> if made right you could cut the machine in half and get two lisp machines
I get where you're coming from in theory, but that's quite far removed from the common usage of the term "lisp machines" (i.e. those which were sold in the 80s), which weren't particularly different from other computers of the time, except for being optimised (in tandem with the OS) for particular workloads (i.e. Lisp programs).