Q --
Agreed. In my present game, where I've been continuously at war for 14 or so years (Mega-Evil, 255 systems...), any new colony in a current (or probably soon) war zone typically emergency-builds a small stack of mines, followed by the usual YSR combination. I'm too lazy to build WPs and ship 'em out.
One such minefield took out a fleet of 15 small Rage ships; I moved the few ships present away from the outpost, the Rage fleet attacked the now "undefended" colony, and was completely obliterated.
But the best defense is generally an offense sufficiently active and powerful to wipe out all nearby colonies that would be useful as staging Posts for attacks on you, combined with lots of intel points to help plug any leaks (CI on an attacking fleet, say). Combine with warp point defenses, except against human players with stellar manipulation and lots of resources (which they probably will have soon, with stellar manipulation...).
------------------
-- The thing that goes bump in the night