... I really like the wide gearing range ... it's ... really ... nice ...
so what I want to do is upgrade ...
Okay, forgive me (a) for chopping up your words so drastically and (b) for not giving the advice you want, but seriously... why upgrade the wheels? Is there something wrong you haven't told us?
Don't get me wrong, upgrading is lots of fun... I'm always doing it myself... but it's not always necessary.
--If you want a Sturmey Archer 8, wait until the new version comes out.
--Alfine / Nexus are good, but my limited experience doesn't indicate that they're all that much better than the SA 8.
--NuVinci is very nice too, but soo heavy.
--None of the above is going to give you as much range as you have now.
--If you go for a different hub system than you have now, you may have to change the crank/chain ring as well. Certainly you can't use the same chain ring for a Sturmey as you would for a Shimano.
My suggestion would be: overhaul the bike, paint only if really necessary, tune up, clean and polish everything, and put it back together into as new condition, and ride it like that for a while before you upgrade anything. And if you find anything about it that's "really nice," don't change it!