Thanks!
I'd bumped into a similar solution after posting: installing a new theme reduced the size of the icons, but left the taskbar enlarged. I reduced the taskbar size to match, so ok, except...
Maybe the theme that messed up the icons had a very large font associated, and the icons size with the font.
Maybe other things resized with the theme font:
As I type this, the font is very large. Under View, it's set to Medium, and the Address text is the right size, about half the size of this text.
When I open a window from one of the systray icons, it's much bigger than before, though the icon is back to normal. I have to drag the window to the right in order to get to some check blocks on the left.
I also have to drag the IE 6.0 screen down to meet the smaller taskbar size.
I'll try your suggestion about dropping to 640 x 480 and going back to 800 x 600 to see if these get resolved.
Too bad there isn't a separate setting for taskbar sizes that would control all these factors at once.
By the way, my usual setting is 800 x 600. My device is a 'Plug and Play Monitor' (actually a Proview 772 17"

and I've been wondering whether to add a new monitor setting (Windows has a driver for Proview 770) and then delete the generic one. Guess one aggravation is enough for one weekend, though.