Of course, Mike Sodrel was a retread in '04 when he upset Baron Hill. That race wasn't even on the radar it was such a surprise.
Well, yes, retreads do sometimes win, but they far more often lose. It's more than just the retread factor. Simmons beat an incumbent Dem in 2000 to take the seat. The seat became 2% more GOP after redistricting. Simmons then beat Courtney by 54% in 2002, and then beat Sullivan (who I thought was a much superior candidate to Courtney) by 54% in 2004. Simmons is more seasoned, has won three elections in three very different political landscapes, and can also claim to have saved Groton.
And another difference between the Simmons and Hill situations is that Simmons has done nothing at all that I'm aware of to get fired. Hill was a casualty of his vote against the Federal Marriage Amendment. Sure, it wasn't on much of anyone's radar (it was on mine) but that upset does have a clear explanation.
To the contrary, Simmons can claim to have saved Groton, which is not some trivial accomplishment. The only reason I can figure why people are predicting a Simmons loss is just the 'national mood' factor. Maybe that'll do it, but there are plenty of incumbents that represent contrary districts who've survived all kinds of shifts in the national mood.
Connie Morrella pops to mind, who wasn't finally done in by electorate mood swings but by redistricting, and then just barely.