Even if you don't like the pollster (and remember this is being commissioned by the more left-leaning paper of the big Chicago dailies) consider that WAA had Durbin up by 15 in late July and about the same double digit spread in June. As Silver has sometimes noted a poll can be useful for seeing trends even if there is a house bias.
WAA's track record in Illinois is execrable. But as you said, I can certainly see any race where the Dem had an unassailable lead earlier in the year, tighten up by 8 points when people tune in and Republicans coalesce behind their candidate, in particular in a year where Dems are not doing well nationally.
That's not entirely true. On 2012 presidential polling they were right in the middle of the pack by 538's analysis.
Yeah, in other states they might not be bad, but in Illinois, they're trash.
Obviously it's going to be closer than expected, but Oberweis is not within striking distance.
