Since you stil collect ideas i allow me to bring MWSnap to your attention:
MWSnap was my favorite from manys bevor i saw SC.
It's freeware too but use the registry.
MWSnap has some good ideas belong to capture regions:
- Zoom preview the area under the cursor (toggle on/off with F6)
- toggle region-selection-edge (top left/down right) with space-key (nifty)
- resize the region area
- fine tune resize with arrow-keys
- cancel with ESC (i know you plan the same