I'd like to believe you're right about Scott Brown, but here are the weak points:
1. The Democrats never thought they'd ever lose the "Kennedy Seat", so they didn't take his candidacy seriously enough in 2008. They'll do anything to get this seat back (hence millions in out of state donations).
2. Scott Brown remains extremely popular, with a favorability rating that usually guarantees reelection, but the argument that appears to be working for the democrats is that this is the seat that could give republicans control of the senate. I heard on a radio talk show last week a caller actually say that they would vote for Brown if he had a "D" after his name, but are concerned about the republicans getting the senate.
Union members have been threatened with fines if they don't vote Warren. The hope is that many union members pretend they will vote for Warren, but when they get in the booth will vote for Brown. This would not be unprecedented. In 2008, union members holding signs for Coakley came up to Brown and told him that they were getting paid to hold the signs, but would be voting for him.
Bottom line is that the polls would have to be way wrong for Brown to get re-elected.
The answer to those who say we would vote for him if he was a democrat is, you should vote for him because he is a Republican. Otherwise, why should President Romney and the Republican Congress do anything for Massachusetts if there aren’t any Republicans fighting for us.
Your last point about secret union Brown supporters who say they will vote for Warren but them pull the lever for Brown in the secrecy of the voting booth is a good point. Now, with the U Mass/ Boston Herald poll (published 11/5) showing Brown up by 1%, I see Brown with a solid chance of victory. If Romney does better than expected, he will do better in Mass, too, and may even have the coattails to pull Brown to victory. I believe Brown could win with fewer than 1,000 more votes than Warren.
One troubling fact is that undecideds usually break for the challenger. But in this race Brown may be viewed as the underdog/challenger to the Democrat machine.