curved lines are usually the worst. SKP does a poor job of importing curved lines - especially if those lines were drawn as spline curves in your drafting app. there is another ruby script called 'label stray lines' which can also be found in the Ruby Library Depot website.

once you install the Label Stray Lines ruby you can use it to identify the edges which are not closed loops. To do that, select all the edges in the plan first, and go up to Tools > Label Stray Lines. You'll see a bunch of numbered labels that point out which lines are not closed. you can then go through and patch those surfaces. 

There is another ruby called 'Trim_Extend' which, once installed, lives in the context menu (right click menu). But the trim extend function does a poor job of patching curved edges. your best bet is to use the pencil tool for those. 

-mike