the work of the people you cite argue the other way, so no, not those people.
And I want to make it clear that I do not argue that there was no fraud - there are plenty of ways of stealing an election that won't show up in the exit polls anyway, including voter suppression, but also some forms of vote tampering.
But I do think the evidence now weighs fairly heavily against, specifically, large-scale vote switching (i.e. vote switching on a scale to account for the exit poll discrepancy - even a relatively small proportion of it). I laid out this view at some length here
http://www.democraticunderground.com/discuss/duboard.php?az=show_mesg&forum=203&topic_id=398267&mesg_id=398267so I won't repeat it all again.
But in answer to the questions in your last paragraph: it's not the level of a discrepancy that would convince me, but the extent to which it can be "accounted for" (statistically), or not, by convincing factors. For example, had the discrepancy in the Ohio referendum been statistically greater in counties with DRRs I
wouldhave found that fairly persuasive. It was the first thing I thought should be investigated. As Bill Bored says, the null finding from Klinkner's analysis does not rule out fraud, but it infirms one specific (and popular) hypothesis.
I don't believe that exit polls are a very good way to audit an election, although I agree they seem to be all you've got right now. I certainly think that the 2004 exit polls were not designed to do that job, and therefore do it particularly badly. A better designed poll, designed specifically as a check on the election, might work. Ironically Edison-Mitofsky recently conducted such a poll in Azerbaijan.
But I do think it is important for people to be aware that the "Margin of Error" computed for any poll is the Margin of Error
assuming random sampling. No poll can actually assume that, as non-sampling error is a major problem for any survey. Unfortunately you can't calculate it. However, you can examine the methodology fairly carefully, and some polls are simply better than others. The BYU exit poll in Utah was an example of an extremely well designed exit poll. It also got neared to the count in Utah than did the E-M poll.