Speaking of leadership, being single minded can only be a good thing for short periods of time. Since you mentioned Churchill, this was one of the differences he had with Hitler (who was truly single-minded).
It's wrong, I think, to judge a politician by the measure of those who came after him/her. Just because Blair, Major et co. were opportunistic, self-serving, and incompetent doesn't make Thatcher good by itself.
Also, I've been reading analyses to the effect that Thatcher's policies, although maybe beneficial (to some) in the short term, are the sources of many problems of today's UK economy. And Thatcher has not been the only isolationist anyway. Nor are Spain, Greece, Ireland, Cyprus, Holland, Italy in the place they are in because they followed policies other than the UK's...
But, I say, fuck it. I don't think it needs lots of econ-speak to discuss this one. As Matthew said, "What good will it be for someone to gain the whole world, yet forfeit their soul?". What good is it to have an economic 'progress' if the people are not benefitting from it (like it's been happening in Germany for a few years now)? And this is the single-mindess that's so condemnable: she cared only for the economy and forgot about the people, really.