All comments/suggestions/wisdom welcome.

I rarely have any wisdom to offer anyone, but I must agree with Peter's
comments. You'll save money and get better performance using a dedicated radio
each for HF and VHF/UHF.
As a former R8B user (money and circumstance got screwy, but I used it
enthusiastically for two or three years) I can tell you that radio is simply
fabulous, but you already know that. :-)
Save a good chunk of money and get yourself a second, dedicated V/UHF rig, but
ONLY if you find the Uniden wanting. I have not used the 780xlt, but reviews
from users seem to be pretty happy... so if you want a different scanner,
that's your business, but if you're getting the signals you want, stick with
it.
You can then get really creative designing you antenna 'farm', switching
between them for various ranges, etc., but you'll be FAR better off with such a
set-up than with Yaesu's abysmal VR5000, and better off performance-wise and
price-wise than even the (mostly-beloved) Icom R8500. Unless you need
portable/otherwise mobile reception of a wide range of freq's, stick with what
you've got.
There's really not anything above 1.2 GHz that you could/would want to listen
to, unless you're a truly die-hard digital/decoding/data burst hobbyist, and
even then, the pickings are pretty slim regardless of your location. In my
view, not worth the price of the one or two decent wideband radios to get more
spectrum that you won't really listen to.
Good luck-
Linus