See also: Locator beacon
Was thinking of what else would be interesting to add, and remembered compasses always point to your original spawn. Quick search here and only the linked thread directly related to the idea.
General idea is to right-click with a compass (or an "advanced" version) to reset the target to either the block you're on, or the block pointed to (new base far from spawn, distant resource area).
A more advanced compass could possibly have a GUI with a list of "learned" destinations, one of which could be selected as the "active" target (possibly checking if homing target is active/exists/has power/is redstoned/whatever).
Brethern beat me to the idea, I'm just bringing it to suggestion forum and fleshing it out a bit.