tedster - 8:20 pm on Nov 23, 2011 (gmt 0)

I would not suggest switching to a US target in WMT - yes, it may well have a negative affect on your European and Australian traffic.

If you think the non-converting traffic is not worth dealing with, you might consider block it at the server level in .htaccess. But once you switch your WMT targeting away from "unlisted" it can be a monster problem ever to go back if the traffic loss is significant.