To my way of thinking, the “icosphere and dupliverted lights” is more-or-less what Ambient Occlusion is able to replace. And both of these seem to be geared more toward soft, even lighting than for soft shadows.
“Shadow-only spots” are a very handy thing for getting shadow effects. You can use cheaper-to-calculate lights for the overall effect, then add a few shadow-spots to place the necessary shadows only where you want them. Fewer lights equals reduced render-time; especially spots.
You can usually “cheat” shadows, putting less shadows in than might really be there but focusing your attention on the shadows that really matter. In the real world, ambient light bounces around a lot and fills in a lot of shadows, but there remain a few shadows whose purpose is essential for defining depth, 3-D relationships and so-on. The eye will accept the absence of a lot of details which are “technically correct” as long as it does not encounter any jarring omissions or a breakdown of the 3D illusion. (Unless your name is M. C. Eischer, you don’t want that to happen.)
You can also “cheat” lights by using layers and specifying that the light should cast its beam only on certain layers. Ever wanted a light that could shine right through one thing and hit something else? You got it! Unlike school, you won’t get in trouble for “cheating” on a render, and it might save hours of render time. Visualize what you want the scene to look like and figure out the cheapest way to get “good 'enuf.” Then ship it.
Note: The Blender Documentation page at http://www.blender.org/modules/documentation/htmlI/x5888.html is the “bible” for this and lots of other related lighting topics.