I've used medleys at the end of an evening quite frequently, usually
with no walk-through (maybe some mention of a key move), sometimes
with no advance warning (and occasionally without advance planning!).
Usually I use just two very straighforward dances, with the idea that
either of them might be just a little boring by itself to go full
length, since it's mostly the experienced folks left, but that the
crowd has run out of the mental gas to really do anything much more
challenging. The dances are simple, but the dancers feel sufficiently
challenged by there being little or no walk-through, and the change in
the middle is another pick-me-up. The dancers haven't struggled, but
they finish feeling like they've accomplished something.
I agree that you need to be cautious about similarity between the
dances. If they're too similar, it's confusing and probably boring. If
they're relatively simple and mostly different, you won't need to call
too much, except to remind people what comes next after any similar
moves. If you don't have to call much, there's no conflict with the
band and their "hot finishing tunes".
~ Becky Nankivell
Tucson, Ariz. and Long Beach, Calif.