Well, the issue from our point of view is that a lot of what we care about
testing is extremely low-level hardware behavior, like whether spinlocks
work as expected across processors. It's not clear that a simulator would
provide a sufficiently accurate emulation.
OTOH, the really nasty issues like cache coherency rules don't arise in
single-processor systems. So unless you have a multiprocessor VAX
available to spin up, a simulator may tell us as much as we'd learn
anyway.
(If you have got one, maybe some cash could be found --- we do have
project funds available, and I think they'd be well spent on testing
purposes. I don't make those decisions though.)