hmm I can think of a few things:
1) try adding color and thickness: i.e.
#asset-index-desc .container
div
li
:border 1px dashed red !important
2) I presume that the code you provided is not as it appears in your document as otherwise you would get a Sass error about the div tag being too deeply nested.... :)
3) the following does NOT work in my own app,
#sidebar
div
li
border: 1px dashed red !important
BUT if I remove the div tag, then it's all good:
#sidebar
li
border: 1px dashed red !important
Hope this helps.....
I LOVE Sass and blueprint.... Especially with compass gem. It takes all of the pain out of styling....