Kennedy's declining health is probably the best thing to happen to Kerry. All the voters who were thinking "eh, I think it's time to replace Kerry and try something new" are now probably saying "we'll just save the new blood to replace Ted."
Do you think Mitt Romney could still win in Massachusetts or did his disaster of a Presidential run tarnish his image there?
For voters to be considering "new blood," new blood would actually need to be running. Kerry is facing a nobody in the primary and then a nobody in the general.
And no, Mitt Romney's unfavorables began spiraling out of control once he announced the Presidential bid. He's got the support of a chunk of the state GOP (though note that McCain did quite well here in the Presidential Primary), and a solid segment of the suburban/exurban Indies, but no support amongst Democrats. To get anywhere as a Republican, you need at least some crossover appeal.
Romney had it in 2002. No longer.
