I find myself having to often switch between the Selection tool and other tools, for example when building walls (Rectangle tool), positioning them (Move tool), and then removing unwanted segments (Selection tool).
I end up with an uncomfortable hand position in order to switch quickly back and forth using keyboard shortcuts.
As soon as I inadvertently slightly move my shortcut hand, I have to actually take my eyes off the screen and look down at my keyboard. It turns into a huge waste of time and forces me to break attention with what I was doing with my model.
In the same way that Adobe Illustrator allow a user to hold ctrl (windows) or command (mac) in order toggle on the selection tool, it would be a major improvement in Sketchup to be able hold the spacebar in order to temporarily switch to the Selection tool. Modifier keys for the Selection tool should also become available when in this toggled on mode.
When you release the space bar, the Select Tool toggles off and you are back with the tool you were on, of course.